WebNN: avoid staging buffers on first inference

Fixes an issue where a staging buffer was always created on first use because its last used fence value was initially set to UINT64_MAX which could never be considered "not in use" until a submission occurred first. Instead, this fence value should of been set the initial value of the queue's fence, which is considered "not in use" without requiring a submission first.

Bug: 358594662
Change-Id: I960d4b55f468f92a8a34bcae896816f2d5e18fc6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5777470


Commit-Queue: ningxin hu <ningxin.hu@intel.com>
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1339981}