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

[bruvzg]

Adds support for importing TTC and OTC files, adds face_index import property as well as TextServer methods to select face index and get the number of faces.

Screen.Recording.2022-06-07.at.11.06.45.mov

face_index can be made selectable at runtime as a part of #61406 / #61473 if it's desired, but the primary goal of this change is implementing godotengine/godot-proposals#306 (in particular, significant part of macOS system fonts are shipped as TTC and OTC collections).

[fire]

The feature proposal for this look wanted to support the Apple ecosystem.

Not that familiar with the Godot Engine font server.

[akien-mga]

Thanks!

[lmurray]

This PR introduced a 14% performance regression for editor startup, at least for me on Windows when using the fallback text server.

c:\src\games>hyperfine -iw2 -r10 "out\Godot_fonts.exe --quit pong\project.godot" "out\Godot_prev.exe --quit pong\project.godot"
Benchmark 1: out\Godot_fonts.exe --quit pong\project.godot
  Time (mean ± σ):      3.398 s ±  0.021 s    [User: 0.001 s, System: 0.003 s]
  Range (min … max):    3.373 s …  3.434 s    10 runs

  Warning: Ignoring non-zero exit code.

Benchmark 2: out\Godot_prev.exe --quit pong\project.godot
  Time (mean ± σ):      2.975 s ±  0.021 s    [User: 0.004 s, System: 0.004 s]
  Range (min … max):    2.942 s …  3.005 s    10 runs

  Warning: Ignoring non-zero exit code.

Summary
  'out\Godot_prev.exe --quit pong\project.godot' ran
    1.14 ± 0.01 times faster than 'out\Godot_fonts.exe --quit pong\project.godot'