[WebGPU] Metal shader compilation should assert for fuzzer builds
<rdar://problem/118939290>
Pull request: https://github.com/WebKit/WebKit/pull/21059
Committed 271310@main (d8d8ad4f40f8): <https://commits.webkit.org/271310@main> Reviewed commits have been landed. Closing PR #21059 and removing active labels.