Add missing font file filters in hint string

[beicause]

Adds the missing *.ttc *.otc in hint string for selecting font files, which are supported by:

• [TextServer] Adds support for TrueType / OpenType collection files (*.TTC, *.OTC). #61772

[KoBeWi]

It would be nice to automate it somehow, instead of hard-coding.
Unfortunately get_recognized_extensions_for_type("FontFile") returns also image files, not sure how to get only supported fonts.

[bruvzg]

Adding *.ttc *.otc without adding (and using when loading the font) face_index properties for the same editor fonts is not useful. These types are font collections and simply selecting the file will always use the first font in collection.

[beicause]

I decide to close this. Not being able to select face index makes font collections not useful for editor and default theme font. We can add face index to editor settings and project settings, but it is kind of niche.

As a workaround for default theme font, face index can be set in a custom FontVariation, but this cannot be used for the fonts of editor.

As a workaround if you still want to use the first font in collection, you can force to select all files (*).