Update CustomElementsRegistry.prototype.getName to return DOMString instead of unconventional DOMString or undefined.
Pull request: https://github.com/WebKit/WebKit/pull/14705
Committed 264916@main (1515a23b954f): <https://commits.webkit.org/264916@main> Reviewed commits have been landed. Closing PR #14705 and removing active labels.
<rdar://problem/110360220>