Move SkBitmap::copyTo() implementation into the framework

This is a refactor.  SkBitmap::copyTo() is a poorly defined
API.  Over time, we've added in various fix-ups to ensure
a certain behavior for the Android framework.  This CL
moves that logic into Android, which is a step toward
removing the copyTo API from SkBitmap.
skbug.com/6464

Test: Copy tests already exist.  Added testing for F16.

Change-Id: I4fe29e209d97eeb15336c9f6226853a408741054