[effects/presentwindows] Allow closing windows on middle-click

Summary:
Plasma's Task manager exposes an optional  feature whereby the user
can middle-click on a window to close it, but the Present Windows effect
does not do the same.

The presence of a close button you can left-click does not replace the desirable
feature to be able to middle-click on a window to close it, because then the
whole window becomes a click target, so it can be much much faster than
having to aim for the little close button. Also it's off by default, so a user
who goes out of their way to turn it on is signaling that they want to accept the
risk of accidentally closing a window by accident.

Finally, the feature is not allowed for left-click, so people can never accidentally
wreck Present Windows for themselves by assigning it to left-click by accident
and then mistakenly closing their windows.

This reverts commit 55585514f9.

FEATURE: 321190
FIXED-IN: 5.17.0

Test Plan:
Set "Close window" in the Present windows effect, trigger effect, and middle-click on window

{F6815303}

Reviewers: #kwin, davidedmundson, broulik, zzag, #plasma, hein, mart

Reviewed By: #kwin, #plasma, mart

Subscribers: mart, abetts, apol, zzag, luebking, kossebau, graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D21083

effects/presentwindows/presentwindows.cpp

@@ -719,6 +719,11 @@ void PresentWindowsEffect::mouseActionWindow(WindowMouseAction& action)
                 m_highlightedWindow->minimize();
         }
         break;
+    case WindowCloseAction:
+        if (m_highlightedWindow) {
+            m_highlightedWindow->closeWindow();
+        }
+        break;
     default:
         break;
     }

effects/presentwindows/presentwindows.h

@@ -149,7 +149,8 @@ public:
         WindowExitAction = 2, // Deactivates the effect without activating new window
         WindowToCurrentDesktopAction = 3, // Brings window to current desktop
         WindowToAllDesktopsAction = 4, // Brings window to all desktops
-        WindowMinimizeAction = 5 // Minimize the window
+        WindowMinimizeAction = 5, // Minimizes the window
+        WindowCloseAction = 6 // Closes the window
     };
     enum DesktopMouseAction {
         DesktopNoAction = 0, // nothing

effects/presentwindows/presentwindows_config.ui

@@ -208,6 +208,11 @@
           <string>(Un-)Minimize window</string>
          </property>
         </item>
+        <item>
+         <property name="text">
+          <string>Close window</string>
+         </property>
+        </item>
        </widget>
       </item>
       <item row="2" column="0">
@@ -252,6 +257,11 @@
           <string>(Un-)Minimize window</string>
          </property>
         </item>
+        <item>
+         <property name="text">
+          <string>Close window</string>
+         </property>
+        </item>
        </widget>
       </item>
      </layout>