This forces a hard limit on the buffer size we allocate from D3D11. It
can work around a D3D11 driver bug on NVIDIA where we would get an
invalid map pointer. This seemed to happen when the buffer sizes were
close to MAX_UINT.

Bug: chromium:943087
Change-Id: I64aa9c55cbb82015101262c19c72741c140964a5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1531374
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>