Reset the queue in ScreenCapturerX11 when updating monitors.

This is a speculative fix for the DCHECK at the top of
ScreenCapturerX11::CaptureScreen(). Whenever |selected_monitor_rect_|
changes, |queue_| should be reset, so that new frames are allocated
with the correct size. This CL adds a reset to UpdateMonitors() which
modifies |selected_monitor_rect_| and is called whenever an X11
configuration-change event is received (for example, when a monitor is
resized).

Bug: chromium:1372579
Change-Id: I9cc84a8b6990802f9d7dde05966ee17a80ddd48e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279065
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Lambros Lambrou <lambroslambrou@chromium.org>
Auto-Submit: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/main@{#38374}