[plugins/dialogparent]: Disable darkening while picking colors
Integrate with colorpicker effect to disable window darkening while color picker effect is active. Unfortunately, this solution has couple of limitations:
- active state of effects is not an observable property, so a new property had to be added to the effects singleton;
- consequently, list of active effects is not an observable property, so the whole thing could not be implemented in pure QML in the dialog parent effects;
- actual isActive() state of the color picker for whatever reason required that m_scheduledPosition is not an invalid point, effectively making it always inactive except for a brief moment between addRepaintFull() call and paintScreen() callback. That check had to be removed.
- QColorDialog windows are still modal and darkened by default;
- QColorDialog on X11 does not use portals/KWin, so this trick does not apply at all;
- effects->isScreenLocked() which isActive() depends on is not an observable property either.