[DO NOT MERGE] Update FreeType to 2.6.2 + update 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 (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://googleplex-android-review.git.corp.google.com/#/c/846889

An AOSP master CL 
(https://android-review.googlesource.com/#/c/196504/) is ported
to mnc-dev.

Bug: 24296662

Change-Id: Iec6784838d89098f332e6d1ed79663efd91a8441
Signed-off-by: Jungshik Shin <jungshik@google.com>
188 files changed