Android CTS 7.0 Release 14 (4372023)
Update harfbuzz to 1.2.6 from 1.2.1

Chromium moved to 1.2.6 in ToT and it's recommended by
the upstream (Behdad).

For the acutal changes, see

https://android.googlesource.com/platform/external/harfbuzz_ng/+log/dabf32a5ad..00ea66

There's no change in 'rl' files so that there's no change in the
corresponding generated header files, either.

Android.mk was updated along with src/hb-version.h and README.version.

BUG: 28006027

Change-Id: I96068caae7b98d5665b0c71918f1b50deb428e2b