Add android.Paint that inherits SkPaint

The idea is that extra paint parameters that only affect text layout
(not rendering) will go in android.Paint instead of going into
SkPaintOptionsAndroid.  We will eventually move those out of SkPaint
too.

This is currently implemented in PaintImpl.cpp.  Will be renamed when
current Paint.cpp that has JNI bits is moved to android_graphics_Paint.cpp.

Change-Id: Iba66c34dea5da503a13b9c864cb9f2211ac4ba7d