If an output is powered on/off while connected the available workspace must be resized to have no "dead" areas.

Currently this is only done when an output is (dis-)connected or en/disabled.

Question: Should we just move it out of m_enabledOutputs then or leave it there but add a flag or set its logical size to invalid?

Plan1:

1. KScreen listens via DPMS protocol for DPMS changes.
2. KScreen sends logical geometry information to KWin.
3. KWin updates size.
4. KWin could remove outputs with logical invalid size from enabled outputs for optimization and robustness.

Plan2:

1. KWin automatically moves on/off outputs into/from m_enabledOutputs.
2. KWin resizes overall screen (by which parameters?).
3. Potentially KScreen sends new layout to KWin