Add /data/fonts/files directory

The updated font files will be stored to /data/fonts/files and
all application will read it for drawing text.
Thus, /data/fonts/files needs to be readable by apps and only writable
by system_server (and init).

Bug: 173517579
Test: atest CtsGraphicsTestCases
Test: Manually done
Change-Id: Ia76b109704f6214eb3f1798e8d21260343eda231
5 files changed