screen-cast: Fix monitor recording on HiDPI

screen-cast: Fix monitor recording on HiDPI

It scaled the logical monitor rect with scale to get the stream
dimensions, but that is only valid when having
'scale-monitor-framebuffers' enabled. Even when it was, it didn't work
properly, as clutter_stage_capture_into() doesn't work properly with
scaled monitor framebuffers yet.

(cherry picked from commit 3fa6a92cc5dda6ab3939c3e982185f6caf453360)

Bug: https://gitlab.gnome.org/GNOME/mutter/merge_requests/415
Applied-upstream: 3.30.3, commit:1c57a5842069735b7bb80846130bf61d0e0a0880

Gbp-Pq: Name screen-cast-Fix-monitor-recording-on-HiDPI.patch