Allow WKWebView embedders to load mixed content from localhost
<rdar://problem/126085870>
Pull request: https://github.com/WebKit/WebKit/pull/27086
rdar://125851000
Pull request: https://github.com/WebKit/WebKit/pull/27270
Committed 277709@main (464e3e51f7c8): <https://commits.webkit.org/277709@main> Reviewed commits have been landed. Closing PR #27270 and removing active labels.