Re-enable generation of wxEVT_MOVE_{START,END} events under wxMSW.

Handling of WM_{ENTER,EXIT}SIZEMOVE was disabled as a side-effect of r47927,
possibly unintentionally. Revert this change to generate these events again.

Also document that they're MSW-only for now.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66846 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -2727,7 +2727,7 @@ WXLRESULT wxWindowMSW::MSWWindowProc(WXUINT message, WXWPARAM wParam, WXLPARAM l
                 }
             }
             break;
-#if 0
+
         case WM_ENTERSIZEMOVE:
             {
                 processed = HandleEnterSizeMove();
@@ -2739,7 +2739,7 @@ WXLRESULT wxWindowMSW::MSWWindowProc(WXUINT message, WXWPARAM wParam, WXLPARAM l
                 processed = HandleExitSizeMove();
             }
             break;
-#endif
+
         case WM_SIZING:
             {
                 LPRECT pRect = (LPRECT)lParam;