Use transfer buffer for BatchAtlas texture copies.

Sets up use of transfer buffer (if available) to do one-copy transfers.
Get transfer buffers working properly in GL.
Implement GrVkGpu::onTransferPixels.
Check caps to ensure we can create a transfer buffer.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1888473002

Review URL: https://codereview.chromium.org/1888473002
14 files changed