simplify GrCaps::initDstCopyDesc and provide default impl for non-GL
subclasses.

Change-Id: I0397d6fc62ca95d3970ec491e198ca547902e691
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/228258
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
8 files changed