D28781: Add 'Activate clicked window' toggle in Desktop Grid effect

[Konstantinos Smanis]

ksmanis created this revision.
ksmanis added reviewers: KWin, VDG.
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REVISION SUMMARY
  Currently, the clicked window is unconditionally elevated and activated in the Desktop Grid effect. This patch adds a configuration toggle that controls this behavior, allowing the user to select a virtual desktop without worrying about disrupting the previously active window.
  
  When the toggle is on (default), no change in the current behavior is observed, except that windows are not immediately elevated when clicked, but rather after maintaining the click for `QApplication::startDragTime()` [1]. This change was introduced for the sake of consistency, since a timeout is required for the scenario that the toggle is off, in order to avoid window flickering caused by unnecessarily elevating a non-activated window. In other words, with the previous behavior, the clicked window would be immediately elevated, since it would end up being activated anyway. With this patch, the clicked window might not end up being activated, so we postpone elevating it until we are sure that it will also be activated.
  
  When the toggle is off, the clicked window is not activated. Therefore, the user returns to an unchanged virtual desktop irrespectively of where he/she clicked in it.
  
  [1] Dragging windows always results in them being activated.

TEST PLAN
  Screencast of current behavior (starts with default configuration for Desktop Grid effect):
  F8232947: desktopgrid-2020-04-12_15.54.59_before.mp4 <https://phabricator.kde.org/F8232947>
  
  Screencast of patched behavior (starts with default configuration for Desktop Grid effect, i.e., the toggle is turned on, i.e., backwards compatible behavior):
  F8232955: desktopgrid-2020-04-12_16.16.16_after.mp4 <https://phabricator.kde.org/F8232955>

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D28781

AFFECTED FILES
  effects/desktopgrid/desktopgrid.cpp
  effects/desktopgrid/desktopgrid.h
  effects/desktopgrid/desktopgrid.kcfg
  effects/desktopgrid/desktopgrid_config.ui

To: ksmanis, #kwin, #vdg
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