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

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

Unfortunately, forwarding MSW messages only takes care of the menu events but
not the toolbar ones -- which should be handled in the same way but were not.

So restore the old behaviour, the problem with menu items disabled in the
parent frame but enabled in the child one will be fixed differently.

This reverts r73927.

See #14314.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74274 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775