WebNN: Support gruCell MLOperator

This CL adds the IDL and mojo definition for gruCell and implements
`MLGraphBuilder::gruCell()`.

This CL also adds gruCell validation tests in WPT and unit tests in
`WebNNGraphImplTest`.

Bug: 40206287
Change-Id: I0873a5c979bdd3e44a0dd30cba7a53410141ef78
Cq-Include-Trybots: luci.chromium.try:gpu-fyi-try-win11-qualcomm-rel-64, win11-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5376901


Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Reviewed-by: Austin Sullivan <asully@chromium.org>
Commit-Queue: Bin Miao <bin.miao@intel.com>
Cr-Commit-Position: refs/heads/main@{#1280572}