webnn: Implement gather op with a different gather variant in CoreML
Almost all gather WPTs were failing on Mac, but this wasn't apparent
because most of the test used int64 indices, which are not supported on
CoreML. To increase coverage of the CoreML backend, this CL also updates
the gather WPTs to predominantly use int32 indices
After this CL, the only remaining failures are WPTs which use scalar
indices. These failures will be investigated in a follow-up CL
Bug: 41481333
Change-Id: I8a0f4b32aa406512d0c396d8251d39f78149c295
Cq-Include-Trybots: luci.chromium.try:mac15-blink-rel,mac15.arm64-blink-rel,mac14-blink-rel,mac14.arm64-blink-rel,win11-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5935993
Commit-Queue: Austin Sullivan asully@chromium.org
Reviewed-by: ningxin hu ningxin.hu@intel.com
Cr-Commit-Position: refs/heads/main@{#1370061}