Add new RGBA_F16 bitmap config

This configuration uses 64 bits per pixel. Heach component is stored as a
half precision float value (16 bits). Half floats can be decoded/encoded
using android.util.Half.

RGBA_F16 bitmaps are used to decode wide-gamut images stored in 16 bit
formats (PNG 16 bit for instance). aapt is currently not aware of PNG
16 bits so such files must be placed in raw/ resource directories.

This first pass provides only partial drawing support with hardware
acceleration. RGBA_F16 bitmaps are stored in linear space and need
to be encoded to gamma space with the appropriate OETF to be rendered
properly on Android's current surfaces. They are however suitable for
linear blending. Full rendering support will be provided in a future
CL (BitmapShaders might be a bit tricky to handle properly during
shader generation).

Bug: 32984164
Test: bit CtsGraphicsTestCases:android.graphics.cts.BitmapRGBAF16Test

Change-Id: I328e6b567441a1b9d152a3e7be944a2cf63193bd