Add the ability for the IPCTestingAPI to report when a sync stream message fails to be deserialized correctly
<rdar://problem/118391408>
Pull request: https://github.com/WebKit/WebKit/pull/20481
Committed 270892@main (56b0d92bb3fe): <https://commits.webkit.org/270892@main> Reviewed commits have been landed. Closing PR #20481 and removing active labels.