Replace generated media type map with hand-maintained array

[jimsafley]

See #2488

The media type map (used to guess file extensions from MIME types when an uploaded file has no extension) was previously generated by fetching Apache's mime.types and converting it via a script. This worked but had drawbacks: alphabetical ordering from Apache meant poor extension choices (e.g. mpga instead of mp3), an override system was needed to paper over those choices, and the array format was raw var_export output.

This replaces that tooling with a hand-maintained array:

• Drops the generation script, gulp task, and CS fixer exclusion
• Moves the file next to the factory that uses it
• Simplifies from string => string[] to string => string (the map is only used for extension guessing, not validation)
• Chooses conventional extensions throughout rather than deferring to Apache's alphabetical order
• Comments out obscure types unlikely to be uploaded, while keeping all original entries in the file for reference
• Ensures all types and extensions in the upload allowlists have active entries
• Adds the following types that were in the allowlist but absent from the Apache source:
  • application/vnd.ms-access → mdb
  • application/vnd.ms-write → wri
  • application/x-gzip → gz
  • application/x-ms-wmp → wmp
  • audio/opus → opus
  • audio/x-realaudio → ra
  • image/pjpeg → jpg
  • video/divx → divx