WebGPU: Remove ASSERT in depth/stencil clears Instead of asserting that we are not clearing depth or stencil, just log an UNIMPLEMENTED and skip the call. This allows many dEQP tests to run without crashing on the ASSERT. Bug: angleproject:356399840 Change-Id: Icfe7a77d7128e679501da42023601217c7b0e6c8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5748445 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>