Analyse whether Fontations meets requirements of FontConfig

Filing this issue to track FontConfig's font parsing and other dependencies on FT in order to estimate complexity of removal of FreeType in Chromium.

@behdad helpfully provided pointers to FontConfig's use of FreeType:
https://github.com/behdad/fontconfig/blob/master/src/fcfreetype.c
https://github.com/behdad/fontconfig/blob/master/fontconfig/fcfreetype.h

The second header is part of FontConfig's public API.

For removal of FreeType in Chrome, we'd need to find replacements for this functionality through Skrifa and read-fonts.

Since FontConfig exposes `FT_Face` at its own interface, I am not sure if changes to FontConfig's interface are needed, and whether FC uses the functions in `fcfreetype.h` internally.