support current standard font mimetypes in matroska metadata

[bfhpx4hjah]

Summary of the bug:

Only legacy font mimetypes are recognized in matroska mimetype metadata tags. E.g. a truetype font is only recognized if the mimetype metadata tag is "application/x-truetype-font", the current standard "font/ttf" isn't recognized.
One problem resulting from this is that when using the subtitles filter, fonts tagged with current standard mimetypes won't be used and subtitles thus might be rendered incorrectly.
The current standard mimetypes for fonts can be found here: ​https://www.iana.org/assignments/media-types/media-types.xhtml#font
Mkvtoolnix-gui uses these mimetypes for fonts by default, any matroska file created by it containing attached fonts will exhibit this issue (unless the option to use legacy mimetypes for fonts is enabled or an old version of mkvtoolnix-gui is used).

How to reproduce:

Create a matroska file with an attached font using a recent version (58.0.0 or later, based on my testing) of mkvtoolnix-gui and try to open the file with ffmpeg:

% ffmpeg -i mime_current.mkv
ffmpeg version N-103603-gc4973e2148
built on arch linux
...
[matroska,webm @ 0x562ab0532b40] Could not find codec parameters for stream 1 (Attachment: none): unknown codec
...
  Stream #0:1, 0, 1/90000: Attachment: none
    Metadata:
      filename        : NotoSans-Regular.ttf
      mimetype        : font/ttf
...

Simply changing the mimetype metadata tag to the legacy value (e.g. using mkvpropedit or the edit headers tool in mkvtoolnix-gui) will solve the issue:

% ffmpeg -i mime_legacy.mkv
ffmpeg version N-103603-gc4973e2148
built on arch linux
...
[matroska,webm @ 0x55649aa2eb40] All info found
...
  Stream #0:1, 0, 1/90000: Attachment: ttf
    Metadata:
      filename        : NotoSans-Regular.ttf
      mimetype        : application/x-truetype-font
...

[Balling]

Well, that is just a bug here. ​https://github.com/FFmpeg/FFmpeg/blob/9abf0e0419c1ebfe6ba9075af0f032b6d45ef741/libavformat/matroskadec.c#L790

[mkver]

I actually wanted to do this as soon as there is official agreement about this ​here. But it seems that the "soon(ish)" there can be pretty long, so I will just add all the mime types even without an official list.

[Balling]

Is this enough? af6081273f483844fc055bc8623ec07198462c2a