Add a new api to VulkanMemoryAllocator.

Add a new api to VulkanMemoryAllocator to query total allocated
and used vma memory by a single query.

Change-Id: I91a8a64680a57f5cb06b16d9800d79cfd5175d52
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/616158
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
4 files changed