Update FreeType to a512b0fe7a from 2.6.0

1. Update to a512b0fe7a (several patches past 2.6.2). Major changes include
   - stem-darkening is OFF for CFF fonts by default
   - general code tightening
   - header file location is back to include/freetype (they used be include/)
2. A bit more details are added to README.android for the reference.

This CL requires a pdfium change (the way it includes FT header
files : https://android-review.googlesource.com/#/c/196608/ )

BUG=24296662

Change-Id: I9d52999c4c5371e70802907eb47205d8e7b0e581
Signed-off-by: Jungshik Shin <jungshik@google.com>
188 files changed