…nes in the whole solution (#7931)

(This PR is actually
#7697 that accidentally
got closed)

## Context

Part of **Configuration Inversion (Step 5)** - Stack progress:
1. [#7548](#7548) - Add
GitLab step and JSON configuration file
2. [#7688](#7688) -
Cleanup configuration / platform keys + source generator
3. [#7698](#7698) -
Aliases handling via source generator
4. [#7689](#7689) -
Analyzers for platform and ConfigurationBuilder
5. **→ [#7931](#7697) -
Replace manual ConfigurationKeys by generated ones in the whole solution
(this PR)**
6. [#7932](#7932) -
Forbid use of System.Environment methods and adapt everywhere
7. [#7937](#7937) -
Integration names to generated keys

## Summary of changes

Fixed the
[ConfigurationKeysGenerator](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace.SourceGenerators/Configuration/ConfigurationKeysGenerator.cs:21:0-958:1)
to properly read and apply the
[configuration_keys_mapping.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/configuration_keys_mapping.json:0:0-0:0)
file, and extracted common file header comments to a reusable constant.

**Key changes:**
- Fixed JSON array extraction in
[ParseMappingFile](cci:1://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace.SourceGenerators/Configuration/ConfigurationKeysGenerator.cs:350:4-524:5)
method - the generator was incorrectly trying to extract the
`"mappings"` field as an object instead of an array
- Extracted configuration generator comments to
`Constants.ConfigurationGeneratorComment` for reuse across multiple
generators
- Updated both
[ConfigurationKeysGenerator](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace.SourceGenerators/Configuration/ConfigurationKeysGenerator.cs:21:0-958:1)
and
[ConfigKeyAliasesSwitcherGenerator](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace.SourceGenerators/Configuration/ConfigKeyAliasesSwitcherGenerator.cs:24:0-340:1)
to use the shared constant
- Added documentation as to how to add a key now

## Reason for change

The
[configuration_keys_mapping.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/configuration_keys_mapping.json:0:0-0:0)
file was being ignored during code generation, causing the generator to
produce incorrect constant names. This meant that any manual edits to
constant names in the mapping file were not being respected, and the
generated code would use auto-generated names instead of the explicitly
mapped ones.

Additionally, the file header comments explaining that files are
auto-generated were duplicated across generators, violating DRY
principles.

## Implementation details

1. **Fixed array extraction logic**: Replaced the call to
[JsonReader.ExtractJsonObjectSection()](cci:1://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace.SourceGenerators/Configuration/JsonReader.cs:16:4-91:5)
with custom array extraction code that:
   - Finds the `"mappings":` key in the JSON
   - Locates the opening `[` bracket
   - Tracks bracket nesting to find the matching closing `]`
   - Extracts the complete array content

2. **Resolved variable scope issue**: Reused existing `inString` and
`escapeNext` variables from the outer scope instead of redeclaring them,
fixing compilation errors.

3. **Centralized header comments**: Created
`Constants.ConfigurationGeneratorComment` containing the standardized
auto-generation notice and updated both generators to use it.

## Test coverage

- Verified the generator builds successfully without errors
- The mapping file is now properly parsed and applied during code
generation
- Generated constant names now match the mappings defined in
[configuration_keys_mapping.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/configuration_keys_mapping.json:0:0-0:0)

## Other details

This fix ensures that the explicit naming conventions defined in
[configuration_keys_mapping.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/configuration_keys_mapping.json:0:0-0:0)
are respected, maintaining consistency with the existing codebase and
preventing future confusion when constant names don't match their
expected values.

---------

Co-authored-by: Andrew Lock <andrew.lock@datadoghq.com>

…apt everywhere (#7932)

## Context

Part of **Configuration Inversion (Step 6)** - Stack progress:
1. [#7548](#7548) - Add
GitLab step and JSON configuration file
2. [#7688](#7688) -
Cleanup configuration / platform keys + source generator
3. [#7698](#7698) -
Aliases handling via source generator
4. [#7689](#7689) -
Analyzers for platform and ConfigurationBuilder
5. [#7931](#7931) -
Replace manual ConfigurationKeys by generated ones in the whole solution
6. **→ [#7932](#7932) -
Forbid use of System.Environment methods and adapt everywhere (this
PR)**
7. [#7937](#7937) -
Integration names to generated keys

I'll update the PR summary to mention the YAML documentation file:

## Summary of changes

Banned direct `System.Environment.GetEnvironmentVariable()` usage and
migrated all environment variable access to use `EnvironmentHelpers`
with strongly-typed
[ConfigurationKeys](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Generated/net461/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.g.cs:15:0-737:1)
and `PlatformKeys` constants.

### Key changes:
- **Banned `System.Environment.GetEnvironmentVariable()`** via
`BannedApiAnalyzers`
- **Added `EnvironmentGetEnvironmentVariableAnalyzer` (DD0009)** to
enforce
[ConfigurationKeys](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Generated/net461/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.g.cs:15:0-737:1)/`PlatformKeys`
usage only
- **Nested `PlatformKeys` by category** (Ci, Aws, AzureAppService,
ServiceFabric, DotNet)
- **Migrated ~50+ files** across CI Visibility, AWS Lambda, AppSec,
Telemetry, Profiler, and Agent components
- **Added missing keys** to
[supported-configurations.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations.json:0:0-0:0)
and their documentation to
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0)

## Reason for change

Direct `System.Environment.GetEnvironmentVariable()` calls with string
literals are error-prone. Centralizing through `EnvironmentHelpers` with
strongly-typed constants provides compile-time validation,
discoverability, and refactoring safety.

## Implementation details

1. **Banned API enforcement** - Added `BannedSymbols.txt` and configured
`.editorconfig` to treat RS0030 as error (vendored code excluded)
2. **Custom analyzer** - DD0009 validates all `EnvironmentHelpers` calls
accept only
[ConfigurationKeys](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Generated/net461/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.g.cs:15:0-737:1)/`PlatformKeys`
constants, rejecting hardcoded strings
3. **PlatformKeys organization** - Nested by category for better
discoverability
4. **EnvironmentHelpers refactoring** - Added overloads for nested class
constants, maintained backward compatibility
5. **Configuration documentation** - Added missing configuration keys to
[supported-configurations.json](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations.json:0:0-0:0)
and comprehensive XML documentation to
[supported-configurations-docs.yaml](cci:7://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Configuration/supported-configurations-docs.yaml:0:0-0:0),
which the source generator uses to generate XML doc comments in
[ConfigurationKeys](cci:2://file:///Users/anna.yafi/go/src/github.com/DataDog/dd-trace-dotnet3/tracer/src/Datadog.Trace/Generated/net461/Datadog.Trace.SourceGenerators/ConfigurationKeysGenerator/ConfigurationKeys.g.cs:15:0-737:1)
classes

## Test coverage

- ✅ Comprehensive analyzer tests covering valid/invalid scenarios
- ✅ All existing unit tests pass
- ✅ Banned API analyzer correctly flags direct `System.Environment`
usage

## Other details

+2,600/-940 lines. No breaking changes, negligible performance impact.