Transform & preserve gainmaps

Have Bitmap.createBitmap(sourceBitmap, ...) preserve any gainmaps if
present, transforming the gainmaps in the same way.

This addresses 2 common usages:

1) Rotating bitmaps to handle EXIF orientations
2) Bitmap.createScaledBitmap() to do "static" scaling

Bug: 286131154
Test: SilkFX GainmapTransformsTest
Change-Id: I5a62dccbb2c70bc38cca581b161eef792c8b2a78