Fixes genre. Allows for more info to be retrieved on MacOS. Fixes mimeType on Windows/Linux.

[holotrek]

• A lot of info was being missed on MacOS when metadata was edited in Music (formerly iTunes) on MacOS
  • This PR uses the Metadata Key attributes as a fallback in addition to the existing Metadata Identifier
• For Genre, it is modified to no longer require it to be in a specific list of predetermined genres
• Also, a fix was made to the Flutter code to get Genre from the correct map
• The mimeType was fixed on Windows/Linux by adding the "InternetMediaType" key to the list of fields to retrieve from MediaInfo.dll