Currently, key events rely on `FocusController` in the web process to determine which frame should receive a key event. For site isolation, we should reference information on the focused frame stored in the UI process so we can send the key event directly to the web process hosting the focused frame.
<rdar://problem/116167166>
Pull request: https://github.com/WebKit/WebKit/pull/18333
Committed 268639@main (81ab068d217b): <https://commits.webkit.org/268639@main> Reviewed commits have been landed. Closing PR #18333 and removing active labels.