wayland: Update pointer state before ending the drag

ending a drag will update focus. Kwin explicitly resets it to whatever
is now under the mouse now that the implicit grab has ended.

This means no-one sends a pointer up.

Clients (xwayland) don't automatically make leave events count as a
mouse up, because typically you don't get a leave event whilst we have a
grab.

Xwayland also can't track the status of the wl_datasource as it didn't
use it.

This patch shouldn't affect any wayland clients as we don't send a frame event
until the focus changes which is after the dnd_finished events.

BUG: 465444

Testing done:
 - dragged firefox under xwayland tabs out from firefox to the desktop
 - confirmed a new window appeared

src/wayland/autotests/client/test_drag_drop.cpp

@@ -272,7 +272,8 @@ void TestDragAndDrop::testPointerDragAndDrop()
 
     // verify that we did not get any further input events
     QVERIFY(pointerMotionSpy.isEmpty());
-    QCOMPARE(buttonPressSpy.count(), 1);
+    // the release event is sent primarily for xwayland
+    QCOMPARE(buttonPressSpy.count(), 2);
 }
 
 void TestDragAndDrop::testTouchDragAndDrop()
@@ -530,8 +531,9 @@ void TestDragAndDrop::testPointerEventsIgnored()
     QCOMPARE(axisSpy.count(), 1);
     QCOMPARE(pointerMotionSpy.count(), 1);
     QCOMPARE(pointerEnteredSpy.count(), 1);
-    QCOMPARE(buttonSpy.count(), 1);
     QVERIFY(pointerLeftSpy.isEmpty());
+    // the release event is sent primary for xwayland, see BUG 465444
+    QCOMPARE(buttonSpy.count(), 2);
 }
 
 QTEST_GUILESS_MAIN(TestDragAndDrop)

src/wayland/seat_interface.cpp

@@ -714,6 +714,7 @@ void SeatInterface::notifyPointerButton(quint32 button, PointerButtonState state
                 // not our drag button - ignore
                 return;
             }
+            d->pointer->sendButton(button, state, serial);
             d->endDrag();
             return;
         }