webnn: Migrate Pad validation tests to WPTs
This CL adds WPT tests for pad and removes the unit tests
MLGraphBuilderTest.PadTest, MLGraphTestMojo.PadTest and
MLGraphTest.PadTest.
Bug: 327337526, 328026885
Change-Id: Ic24215dea7c4b995719df168000e107064bef3a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5476427
Reviewed-by: Austin Sullivan asully@chromium.org
Commit-Queue: Shanxing Mei shanxing.mei@intel.com
Reviewed-by: ningxin hu ningxin.hu@intel.com
Cr-Commit-Position: refs/heads/main@{#1293535}