D20521: Don't rescale every output every time outputs change

apol added inline comments.

INLINE COMMENTS

> davidedmundson wrote in drm_backend.cpp:517
> :/ then it sounds like you've uncovered a bug!
> 
> From AbstractOutput::setScale:
> 
>   m_waylandOutput->setScale(std::ceil(scale));
> 
> should work the same if not set
> 
>   m_waylandOutputDevice->setScaleF(scale);
> 
> should work the same if not set
> 
>   m_xdgOutput->setLogicalSize(pixelSize() / m_scale);
> 
> really really important to call once, but also called from setWaylandMode looks like it is being called correctly
> 
>   emit modeChanged();
> 
> Is only emitted here and not in setWaylandMode?? Probably our bug.

Tried this, doesn't help.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D20521

To: apol, #plasma
Cc: davidedmundson, ngraham, kwin, jraleigh, GB_2, mkulinski, ragreen, jackyalcine, Pitel, iodelay, bwowk, ZrenBot, alexeymin, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart