backends/drm: don't turn displays on when a display temporarily disconnects
For a variety of reasons, displays in standby can sometimes trigger the detection of a temporary disconnect. In order to not wrongly wake up the system with such a display, detect that scenario and set the 'new' output to dpms off again.
I chose a timeout of one second for this because it's relatively unlikely that you'd intentionally do that and still long enough to hopefully catch most issues with monitors.
I tested this by partially sliding the connector out and then immediately connecting it again, but if someone with a problematic monitor could test it as well that would be good.