Use [EnabledBySetting] in IDL and consult settings() from document in C++
<rdar://problem/103943916>
Pull request: https://github.com/WebKit/WebKit/pull/8285
Committed 258530@main (e48898fa33c5): <https://commits.webkit.org/258530@main> Reviewed commits have been landed. Closing PR #8285 and removing active labels.