Rename WebPage::mainFrameView() to WebPage::localMainFrameView() and introduce WebPage::localMainFrameView().
<rdar://problem/113145893>
Pull request: https://github.com/WebKit/WebKit/pull/16231
Committed 266456@main (37a31aff7bcb): <https://commits.webkit.org/266456@main> Reviewed commits have been landed. Closing PR #16231 and removing active labels.