Add migration API to GrContextThreadSafeProxy

Bug: b/293490566
Change-Id: I821489c1806ec6d27a8c56b1fb522c24c7938f40
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/786116
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
2 files changed