[Bug 45901] Avoid GPU synchronization due to GPU-CPU transfer (Overwatch)

https://bugs.winehq.org/show_bug.cgi?id=45901

--- Comment #9 from Andrew Wesie  ---
Based on the feedback, maybe this should be split in to two patches.

The first patch adds fast path for downloading a GPU texture to a CPU texture
using PBO (e.g. using texture2d_download_data but passing in a bo_address
instead of dst_location).

The second patch adds a special case to texture2d_download_data to use
glReadPixels for compatible textures (e.g. those that have a render target
usage?). Unless we think that getting accelerated glGetTexImage in Mesa is
possible.

I am curious about the support for accelerated glGetTexImage in AMD and NVIDIA
proprietary drivers. I'd imagine it exists since performance is the main
benefit of PBOs.