Vulkan: Add BufferMemoryAllocator class BufferMemoryAllocator class will be responsible for memory allocation for vkBuffers. The original Allocator class remains the wrapper for vmaAllocator. Bug: b/195588159 Change-Id: I26d016e2f8d13ba459d0aa0bd4e1ebf4d0d48251 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3036256 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Tim Van Patten <timvp@google.com>