[MSPAINT] Realize context menu on canvas (#5352)

- Add actions on Right-Click.
- Add ID_POPUPMENU resource menu.
- Use TrackPopupMenu to show the context menu.
- Improve CMainWindow::OnInitMenuPopup to display context menu.
- Add SelectionModel::m_bContentChanged flag to indicate whether the selection content is changed.
- Fix IDM_IMAGEINVERTCOLORS and IDM_IMAGEROTATEMIRROR commands.
CORE-18867

base/applications/mspaint/canvas.cpp

@@ -272,6 +272,11 @@ LRESULT CCanvasWindow::OnLRButtonDown(BOOL bLeftButton, UINT nMsg, WPARAM wParam
             CanvasToImage(pt);
             StartSelectionDrag(hitSelection, pt);
         }
+        else
+        {
+            canvasWindow.ClientToScreen(&pt);
+            mainWindow.TrackPopupMenu(pt, 0);
+        }
         return 0;
     }