Even when the document is in design mode, its shadow trees shouldn't be considered as editable. There are a few test cases failing in editing/other/editable-state-and-focus-in-shadow-dom-in-designMode.tentative.html because of this.
Pull request: https://github.com/WebKit/WebKit/pull/12361
Committed 262563@main (155c4f42d9ef): <https://commits.webkit.org/262563@main> Reviewed commits have been landed. Closing PR #12361 and removing active labels.
<rdar://problem/107595174>