Simplify SkFontHost_FreeType_common.h

1. Split SkTypeface_FreeType into separate header (this CL)

... planned

2. Split out implementations in ...common.cpp
... perhaps refactor as helper functions, not a subclass?

3. Modify client code, to free up Skia to not rely on these

With this change, SkFontHost_FreeType_common.h is *only* included by
- SkFontHost_FreeType.cpp
- SkFontHost_FreeType_common.cpp

External clients do *not* rely on SkTypeface_FreeType

Change-Id: I99933caa828e95da1642475e4f73a2b527a3014b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/801177
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Reed <mike@reedtribe.org>
Reviewed-by: Florin Malita <fmalita@google.com>
Auto-Submit: Mike Reed <mike@reedtribe.org>
19 files changed