SkMesh buffer factories added that make copies of CPU-backed buffers.

Bug: b/254685251
Change-Id: I384e86faa9acc52867440ec789d02d40e32c2b78
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/594805
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
4 files changed