Add the ability to assign an optional code to process warnings +
add additional type checking to ensure that names and codes can
only be strings.

PR-URL: #10116
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michal Zasso <targos@protonmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

The --redirect-warnings command line argument allows process warnings
to be written to a specified file rather than printed to stderr.

Also adds an equivalent NODE_REDIRECT_WARNINGS environment variable.

If the specified file cannot be opened or written to for any reason,
the argument is ignored and the warning is printed to stderr.

If the file already exists, it will be appended to.

PR-URL: #10116
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michal Zasso <targos@protonmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

Assigns a static identifier code to all runtime and documentation
only deprecations. The identifier code is included in the emitted
DeprecationWarning.

Also adds a deprecations.md to the API docs to provide a central
location where deprecation codes can be referenced and explained.

PR-URL: #10116
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michal Zasso <targos@protonmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>