Initial integration of Minikin to framework

With this patch, framework does at least some of its text rendering
using Minikin instead of TextLayoutCache. There's a lot of stuff broken
and not yet implemented, but the phone will boot.

Changes are hidden behind USE_MINIKIN, which should be set in
BoardConfig.mk for the brave. Without that, there are changes to
signatures in JNI methods and so on, but shouldn't be any visible
changes.

This commit also introduces a new abstraction for Typeface:

The new TypefaceImpl abstraction represents the functionality that
corresponds to a Java Typeface object. Currently it is backed by
SkTypeface, but in the migration to Minikin it is a FontCollection
combined with a FontStyle. This patch introduces a USE_MINIKIN
preprocessor switch, so there is no substantial change to existing
Skia-based code, but which lets us start replacing the implementation
with the Minikin version.

Change-Id: I532c4c2d32d4f4c1f349dc1db37caa112af587ea