webnn: Add the lstmCell operator

This CL adds the IDL and mojo definition for lstmCell, implements
`MLGraphBuilder::lstmCell()` and adds validations on services side. The
DirectML backend implementation is shared with lstm.

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

Bug: 40206287
Change-Id: I8c740ffa43f79d4667bddca93a064ab788cf8129
Cq-Include-Trybots: luci.chromium.try:gpu-fyi-try-win11-qualcomm-rel-64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5347306


Reviewed-by: Austin Sullivan <asully@chromium.org>
Reviewed-by: ningxin hu <ningxin.hu@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Auto-Submit: Shiyi Zou <shiyi.zou@intel.com>
Commit-Queue: Shiyi Zou <shiyi.zou@intel.com>
Cr-Commit-Position: refs/heads/main@{#1278827}