[Fenced Frames] Notify user interaction notification for WebContentsObservers.

WebContentsImpl::DidReceiveInputEvent currently returns early if
a RWH doesn't belong to its primary main frame's tree, but not
traverse the an inner frame. This means WebContentsObservers do
not receive notifications for interactions targeted to the fenced
frame.

This CL changes HasMatchingWidgetHost to recognize when a RWH
belongs to an fenced frame, and accept the interaction.

BUG=1302558

Change-Id: I31134aec79324a249f4686507aefa4ebc5f0ce33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3500572
Reviewed-by: Dominic Farolino <dom@chromium.org>
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Cr-Commit-Position: refs/heads/main@{#985204}