xwayland: Move XRandR emulation to the ResizeWindow hook

This restores the handling of the XRandR emulation for Xwayland rootless
where it was before commit fa7b1c20.

Some compositors may trigger a protocol error if the viewport source is
larger than the actual window size, having that handled in the window
resize hook makes sure we do not regress.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
(cherry picked from commit 702a419c)

Part-of: <xorg/xserver!1535>