Make sure to rebuild rustdoc if `src/rustdoc-json-types` is changed

I think `rustdoc-json-types` was more recently split out, so this download-rustc logic became outdated as it wasn't tracked. This PR adds `src/rustdoc-json-types` to be tracked for difference versus upstream, so that we properly rebuild rustdoc if it has changes versus upstream.

Fixes rust-lang#142738.

### Local testing

This is not so easy to test locally because it requires download-rustc. To test this, you need to:

1. Disable `download-rustc` inhibition from bootstrap changes versus upstream, by including `:!src/bootstrap` in https://github.com/rust-lang/rust/blob/255aa220821c05c3eac7605fce4ea1c9ab2cbdb4/src/bootstrap/src/core/config/config.rs#L67-L74.
2. Then, use a config like `profile = "tools"` which by default uses `download-rustc = "if-unchanged"`.
3. Run `./x test tests/rustdoc-json` one time, to "prime" initial build caches.
4. Change the `FORMAT_VERSION` in `src/rustdoc-json-types`, i.e.
	```diff
	diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
	index 1f93895..72a3720c7b4 100644
	--- a/src/rustdoc-json-types/lib.rs
	+++ b/src/rustdoc-json-types/lib.rs
	`@@` -38,7 +38,7 `@@`
	 // are deliberately not in a doc comment, because they need not be in public docs.)
	 //
	 // Latest feature: Pretty printing of inline attributes changed
	-pub const FORMAT_VERSION: u32 = 48;
	+pub const FORMAT_VERSION: u32 = 666;
	```
5. Observe that without this patch, `rustdoc-json` tests fail because `FORMAT_VERSION` mismatch. Observe that with this patch, rustdoc gets properly rebuilt and `rustdoc-json` tests pass.

cc `@aDotInTheVoid`

r? Kobzol

Rollup of 11 pull requests

Successful merges:

 - #142478 (install docs for each target in different directory)
 - #142629 (Add config builder for bootstrap tests)
 - #142715 (correct template for `#[align]` attribute)
 - #142720 (De-dup common code from `ExternalCrate` methods)
 - #142736 (add issue template for rustdoc)
 - #142743 (rustc-dev-guide subtree update)
 - #142744 (Add a mailmap entry for y21)
 - #142758 (Make sure to rebuild rustdoc if `src/rustdoc-json-types` is changed)
 - #142764 (Convert `ilog(10)` to `ilog10()`)
 - #142767 (Some symbol and PathRoot cleanups)
 - #142769 (remove equivalent new method on context)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup of 10 pull requests

Successful merges:

 - #142629 (Add config builder for bootstrap tests)
 - #142715 (correct template for `#[align]` attribute)
 - #142720 (De-dup common code from `ExternalCrate` methods)
 - #142736 (add issue template for rustdoc)
 - #142743 (rustc-dev-guide subtree update)
 - #142744 (Add a mailmap entry for y21)
 - #142758 (Make sure to rebuild rustdoc if `src/rustdoc-json-types` is changed)
 - #142764 (Convert `ilog(10)` to `ilog10()`)
 - #142767 (Some symbol and PathRoot cleanups)
 - #142769 (remove equivalent new method on context)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of #142758 - jieyouxu:rustdoc-json-types, r=Kobzol

Make sure to rebuild rustdoc if `src/rustdoc-json-types` is changed

I think `rustdoc-json-types` was more recently split out, so this download-rustc logic became outdated as it wasn't tracked. This PR adds `src/rustdoc-json-types` to be tracked for difference versus upstream, so that we properly rebuild rustdoc if it has changes versus upstream.

Fixes #142738.

### Local testing

This is not so easy to test locally because it requires download-rustc. To test this, you need to:

1. Disable `download-rustc` inhibition from bootstrap changes versus upstream, by including `:!src/bootstrap` in https://github.com/rust-lang/rust/blob/255aa220821c05c3eac7605fce4ea1c9ab2cbdb4/src/bootstrap/src/core/config/config.rs#L67-L74.
2. Then, use a config like `profile = "tools"` which by default uses `download-rustc = "if-unchanged"`.
3. Run `./x test tests/rustdoc-json` one time, to "prime" initial build caches.
4. Change the `FORMAT_VERSION` in `src/rustdoc-json-types`, i.e.
	```diff
	diff --git a/src/rustdoc-json-types/lib.rs b/src/rustdoc-json-types/lib.rs
	index 1f93895..72a3720c7b4 100644
	--- a/src/rustdoc-json-types/lib.rs
	+++ b/src/rustdoc-json-types/lib.rs
	``@@`` -38,7 +38,7 ``@@``
	 // are deliberately not in a doc comment, because they need not be in public docs.)
	 //
	 // Latest feature: Pretty printing of inline attributes changed
	-pub const FORMAT_VERSION: u32 = 48;
	+pub const FORMAT_VERSION: u32 = 666;
	```
5. Observe that without this patch, `rustdoc-json` tests fail because `FORMAT_VERSION` mismatch. Observe that with this patch, rustdoc gets properly rebuilt and `rustdoc-json` tests pass.

cc ``@aDotInTheVoid``

r? Kobzol