[WebGPU backend] Set explicit compute subgroup size configs in `APIGetInfo`

In WebGPU backend we did not populate the
`AdapterPropertiesExplicitComputeSubgroupSizeConfigs` struct in
`PhysicalDevice::PopulateBackendProperties()`, leaving
its fields at their default value of 0. When `APIGetInfo` checked the
post-condition `DAWN_ASSERT(IsPowerOfTwo(...))`, it failed because
`IsPowerOfTwo(0)` is false.

This patch fixes this assertion failure by supporting the query of
`AdapterPropertiesExplicitComputeSubgroupSizeConfigs` in `APIGetInfo`.

Bug: 413053623
Change-Id: Ibadf26ba117859a17b1a3655e5b5ca9070fcd259
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/297456
Commit-Queue: Shao, Jiawei <jiawei.shao@intel.com>
Reviewed-by: Shrek Shao <shrekshao@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>