Optimize FontFamily fields.

This CL replaces:
1. mFonts (vector, 20B) with pointer (8B) + size (4B).
2. mCmapFmt14Coverage (vector, 20B) with pointer (8B) + size (2B).
3. mSupportedAxes (unordered_set, 40B) with pointer to sorted array
   (8B) + size (2B).

This CL also packs byte fields at the end to minimize padding.

Together, this CL saves ~13 KB (64 bytes * 198) on oriole.

Bug: 174672300
Test: atest minikin_tests
Change-Id: Ib2311c45a9b25fbde265d70dd45051f16a4bf0f3
4 files changed