Retire android::nio_{get,release}Buffer

Removes unused functions nio_getBuffer and nio_releaseBuffer. Motivated
by the observation that nio_releaseBuffer() will fail hard for
java.nio.Buffer instances backed by heap arrays when the buffer
position is non-zero.

Adds doc comments to AutoBufferPointer that is used in the framework.

Adds test cases for short and int buffers BitmapTest.

Bug: b/130390512
Test: m -j100
Test: atest FrameworksCoreTests:android.graphics.BitmapTest

(cherry picked from commit b0461ebb)

Merged-In: I01fb72ed71d46a4ef8c7d3da82319ea57e391dbd
Change-Id: I01fb72ed71d46a4ef8c7d3da82319ea57e391dbd