Reland "Add option to GrGpuBuffer::updateData to *not* discard non-updated area."

This is a reland of commit a9b52ca52a76b35d7b892c49bb20935f604367fc

Original change's description:
> Add option to GrGpuBuffer::updateData to *not* discard non-updated area.
>
> Also support minimal map region in Dawn implementation when onUpdateBuffer uses mapping.
>
> Bug: skia:13427
> Change-Id: I5c8a2872b520e04f8a55085c86430e635da2f43f
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/553585
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

Bug: skia:13427
Change-Id: I04e8a4cba5dd3d77e457a4df2d8c20397c2ae760
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/554997
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
22 files changed