Add a Workspace::findToplevel(QWindow*) method

This allows finding the Toplevel for a QWindow which is on Wayland a
ShellClient and on X11 an Unmanaged. This can be used to simplify
code when a Toplevel is needed for an internal QWindow without having
to do platform specific checks.

autotests/integration/internal_window.cpp

@@ -196,6 +196,8 @@ void InternalWindowTest::testEnterLeave()
     QSignalSpy clientAddedSpy(waylandServer(), &WaylandServer::shellClientAdded);
     QVERIFY(clientAddedSpy.isValid());
     HelperWindow win;
+    QVERIFY(!workspace()->findToplevel(nullptr));
+    QVERIFY(!workspace()->findToplevel(&win));
     win.setGeometry(0, 0, 100, 100);
     win.show();
 
@@ -204,6 +206,7 @@ void InternalWindowTest::testEnterLeave()
     QVERIFY(!workspace()->activeClient());
     ShellClient *c = clientAddedSpy.first().first().value<ShellClient*>();
     QVERIFY(c->isInternal());
+    QCOMPARE(workspace()->findToplevel(&win), c);
     QCOMPARE(c->geometry(), QRect(0, 0, 100, 100));
 
     QSignalSpy enterSpy(&win, &HelperWindow::entered);

workspace.cpp

@@ -1707,6 +1707,19 @@ Toplevel *Workspace::findToplevel(std::function<bool (const Toplevel*)> func) co
     return nullptr;
 }
 
+Toplevel *Workspace::findToplevel(QWindow *w) const
+{
+    if (!w) {
+        return nullptr;
+    }
+    if (waylandServer()) {
+        if (auto c = waylandServer()->findClient(w)) {
+            return c;
+        }
+    }
+    return findUnmanaged(w->winId());
+}
+
 bool Workspace::hasClient(const AbstractClient *c)
 {
     if (auto cc = dynamic_cast<const Client*>(c)) {

workspace.h

@@ -127,6 +127,11 @@ public:
     Unmanaged *findUnmanaged(xcb_window_t w) const;
     void forEachUnmanaged(std::function<void (Unmanaged*)> func);
     Toplevel *findToplevel(std::function<bool (const Toplevel*)> func) const;
+    /**
+     * Finds the Toplevel for the KWin internal window @p w.
+     * On Wayland this is normally a ShellClient. For X11 an Unmanaged.
+     **/
+    Toplevel *findToplevel(QWindow *w) const;
     /**
      * @brief Finds a Toplevel for the internal window @p w.
      *