Made Button accept space key press and release events

Task-number: QTBUG-57853
Change-Id: I33cd09d78e470a85d0f816781e683b7574f673ab
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

src/controls/Private/BasicButton.qml

@@ -167,8 +167,10 @@ Control {
     activeFocusOnTab: true
 
     Keys.onPressed: {
-        if (event.key === Qt.Key_Space && !event.isAutoRepeat && !behavior.pressed)
+        if (event.key === Qt.Key_Space && !event.isAutoRepeat && !behavior.pressed) {
             behavior.keyPressed = true;
+            event.accepted = true;
+        }
     }
 
     onFocusChanged: if (!focus) behavior.keyPressed = false
@@ -178,6 +180,7 @@ Control {
             behavior.keyPressed = false;
             __action.trigger(button)
             behavior.toggle()
+            event.accepted = true;
         }
     }