This class was added in crrev.com/c/3036256. The original intention was
to use VMA to implement buffer suballocation. Because VMA itself does
not support buffer suballocation, I was thinking to use VMA custom pool
to implement it and this class was intended to wrap all these
functionality into one class. But now thanks to Jamie's effort, VMA
exported generic suballocation algorithm via API and we have implemented
buffer suballocation using that virtual allocation API. So this
BufferMemoryAllocator class is really no longer useful. This CL mostly
reverted that CL and flatten out the buffer allocation call to directly
use VMA's Allocator object.

Bug: b/205337962
Change-Id: I0336056e440f39e2ff49fee8e0ff4b1f355cefe4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3244022


Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Charlie Lao <cclao@google.com>