When a user performs a copy between GL buffers, we need to mark the
destination buffer dirty in case that buffer data is used as vertex
data and requires another conversion to be done.

Bug: angleproject:3544
Test: dEQP-GLES3.functional.buffer.copy.*
Change-Id: Ie3196db4feb0f01d0b25c8799312c5f57c1095a2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1863007Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>