WebNN: avoid staging buffers when device supports UMA

Creates buffers as upload-equivalent custom heaps which allows CPU to
directly read/write into them without the use of staging buffers.

Bug: 40278771
Change-Id: I5564bdbb2c8405a34dbf96e27003058e51eb9c5f
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5560367


Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Commit-Queue: Bryan Bernhart <bryan.bernhart@intel.com>
Cr-Commit-Position: refs/heads/main@{#1312945}