Don't send keyboard events to QWindows which have outputOnly property set

Summary:
PlasmaCore.Dialog has a property outputOnly. This is for example used in
KWin's OnScreenNotification. If that property is set KWin should not send
any key events to it, just like for windows with _q_showWithoutActivating.

BUG: 388112

Test Plan: Not yet

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9618

input.cpp

@@ -819,6 +819,9 @@ class InternalWindowEventFilter : public InputEventFilter {
                 if (w->property("_q_showWithoutActivating").toBool()) {
                     continue;
                 }
+                if (w->property("outputOnly").toBool()) {
+                    continue;
+                }
                 found = w;
                 break;
             }