Add wxKeyEvent::IsAutoRepeat()

The new method is currently supported in Qt, Cocoa, MSW ports (i.e. all
major ones except for wxGTK).

Keyboard example updated with a "Repeat" column.

Closes https://github.com/wxWidgets/wxWidgets/pull/2414

src/msw/window.cpp

@@ -6303,6 +6303,8 @@ MSWInitAnyKeyEvent(wxKeyEvent& event,
     event.m_rawCode = (wxUint32) wParam;
     event.m_rawFlags = (wxUint32) lParam;
     event.SetTimestamp(::GetMessageTime());
+
+    event.m_isRepeat = (HIWORD(lParam) & KF_REPEAT) == KF_REPEAT;
 }
 
 } // anonymous namespace