Ensure buffer read operations wait for pending GPU work to
complete. This is only required for unit tests, but required to
ensure correct results in all cases. Also adds support for staging
buffer if GPU memory type is private.
Buffer clearing routine added to support values above 1 byte.
The previous buffer clearing functionality using fillBuffer writes
values to each byte, rather than the full 32 bit uint used by the
GPU API.
Authored by Apple: Michael Parkin-White
Pull Request: https://projects.blender.org/blender/blender/pulls/108757
cddb53558f