Motivation / Problem

A lot of platform-specific code for font handling is mashed into two files with lots of #ifdefs sprinkled around. Separating it makes for more readable code.

Description

OS-specific code is moved into files in the various OS directories. As Fontconfig is only used for Unix-oid systems, it's implementation is moved into os/unix. FreeType code stays in the normal fontcache.cpp file.

Limitations

The current code is quite complicated with how stuff like settings globals are enabled/disabled. This PR simplifies this by always enabling them no matter if TrueType fonts are actually used.

In the best case, the compiler/linker will just strip them out, in the worst case the binaries gets a few bytes larger than needed.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker