Implement GrGpu::transferFromBufferToBuffer on Vulkan

Bug: skia:13427
Bug: skia:12720
Change-Id: I91c2707bda1c3ed6a850627f9187cfc5b4b81517
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/550706
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed