Forbid creation of wxPaintEvent objects from user code

This doesn't work anyhow, so it's better to prevent the code doing this
from compiling instead of getting run-time asserts or worse.

Also simplify construction of these events inside wxWidgets by passing
the window itself to the ctor instead of passing just its ID and calling
SetEventObject() separately later.

For consistency, do the same thing for wxNcPaintEvent too.

src/msw/window.cpp

@@ -5260,8 +5260,7 @@ bool wxWindowMSW::HandlePaint()
 
     paintStack.push(PaintData(this));
 
-    wxPaintEvent event(m_windowId);
-    event.SetEventObject(this);
+    wxPaintEvent event(this);
 
     bool processed = HandleWindowEvent(event);
 
@@ -5280,8 +5279,7 @@ bool wxWindowMSW::HandlePaint()
     // note that we must generate NC event after the normal one as otherwise
     // BeginPaint() will happily overwrite our decorations with the background
     // colour
-    wxNcPaintEvent eventNc(m_windowId);
-    eventNc.SetEventObject(this);
+    wxNcPaintEvent eventNc(this);
     HandleWindowEvent(eventNc);
 
     // don't keep an HRGN we don't need any longer (GetUpdateRegion() can only