Add Bitmap#getHardwareBuffer

Bug: 148155907
Bug: 135299581
Test: TODO

Hidden for now. We'd like to make it an SDK API eventually
(b/148155907).

Internal code is currently calling createGraphicBufferHandle. This is
not something we plan to expose from the UI rendering module, so add a
method to get a HardwareBuffer instead. This is something we were
already planning to add. It seems that clients of
createGraphicBufferHandle really wanted a Parcelable to pass the
HARDWARE Bitmap to another thread. This should satisfy that use case.

Change-Id: Id701f7c7eab37830cd7d2cdb929cbe6ba4eca119