App transitions/thumbnails: Switch to HardwareBuffer

Bug: 148155907
Bug: 150395371
Test: go/wm-smoke

These previously used a GraphicBuffer created from a HARDWARE Bitmap to
parcel the Bitmap. As part of moving UI Rendering into a mainline
module, which will not include/expose GraphicBuffer,
Bitmap#createGraphicBufferHandle is being replaced by
Bitmap#getHardwareBuffer. Switch over to the now public API.

Change-Id: Id714a48a10fd03a03faa371e206e0c478ae1a4b7