webnn: implement gatherElements for DirectML backend
This CL also adds some WPT conformance tests to verify the
implementation.
webmachinelearning/webnn#375 (comment)
Bug: 40206287
Change-Id: I88e6bbdf1fd6156421d8b190ed6be6d3b216962b
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel, mac14.arm64-blink-rel, mac14-blink-rel, mac15.arm64-blink-rel, mac15-blink-rel, linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5811264
Auto-Submit: Shiyi Zou shiyi.zou@intel.com
Commit-Queue: Weizhong Xia weizhong@google.com
Reviewed-by: ningxin hu ningxin.hu@intel.com
Reviewed-by: Weizhong Xia weizhong@google.com
Cr-Commit-Position: refs/heads/main@{#1348676}