force focus to the panel on AcceptingInputStatus

when the containment (or an applet in it)
gains the state Plasma::AcceptingInputStatus
force the focus to the panel window, restoring
the behavior of Plasma4

BUG: 364276

shell/panelview.cpp

@@ -1043,6 +1043,8 @@ void PanelView::statusChanged(Plasma::Types::ItemStatus status)
 {
     if (status == Plasma::Types::NeedsAttentionStatus) {
         showTemporarily();
+    } else if (status == Plasma::AcceptingInputStatus) {
+        KWindowSystem::forceActiveWindow(winId());
     } else {
         restoreAutoHide();
     }