Set NSTextViewAllowsDowngradeToLayoutManager to NO.
<rdar://121082136>
Pull request: https://github.com/apple/WebKit/pull/1232
Pull request: https://github.com/WebKit/WebKit/pull/27655
Committed 277911@main (10bdca14c142): <https://commits.webkit.org/277911@main> Reviewed commits have been landed. Closing PR #27655 and removing active labels.