Forward events to active child at MSW, not wx, level in wxMDIParentFrame.

Forward events to active child at MSW, not wx, level in wxMDIParentFrame.

We want to handle menu (and toolbar) events in the active MDI child before
handling them in the parent frame itself and the existing code achieved this
by forwarding wxEVT_MENU events at wx event processing level to the active
child. However this was not enough as the underlying MSW WM_COMMAND message
was still sent to the parent frame only and this could result in wx event not
being generated at all if the parent frame had a disabled menu item with the
same ID as (an enabled) item in the child frame, see #14314.

So forward WM_COMMAND directly to ensure that the correct window gets the
event in the first place. And this makes wxEVT_MENU forwarding in TryBefore()
unnecessary.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73927 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775