Provide a more useful exception message when a qualified name fails validation.
Pull request: https://github.com/WebKit/WebKit/pull/13508
Pull request: https://github.com/WebKit/WebKit/pull/13519
Committed 263745@main (dcf5f162b488): <https://commits.webkit.org/263745@main> Reviewed commits have been landed. Closing PR #13508 and removing active labels.
<rdar://problem/108978658>