When declarative Shadow DOM is enabled, shadowRootMode IDL attribute should be defined on HTMLTemplateElement
Pull request: https://github.com/WebKit/WebKit/pull/7592
Committed 257887@main (350f4f7ded43): <https://commits.webkit.org/257887@main> Reviewed commits have been landed. Closing PR #7592 and removing active labels.
<rdar://problem/103379307>