Use android::skia::BitmapRegionDecoder

Bug: skbug.com/10154
Bug: 140600285
Test: BitmapRegionDecoderTest in CtsGraphicsTestCases

Skia is renaming this class in https://skia-review.googlesource.com/c/skia/+/287498
Use the new name for this and android::skia::BitmapRegionDecoder.

Convert CopyAssetToStream to CopyAssetToData. It was already using an
SkData, held by an SkMemoryStream. Using an SkData directly will allow
sharing it with other decoders for a multithreaded BitmapRegionDecoder.
Remove comment about ref/reopen-ing the asset.

Change-Id: Ib51a8d697ad0f5dc1f461257311b31443b5f9dfb