Fix menu event handlers calling order.

Fix menu event handlers calling order.

Pass the menu event to the window associated with the menu first, before
falling back on wxApp.

This required adding yet another flag to keep state in wxEvent but it seems to
be unavoidable as wxMenuBase::SendEvent() calls ProcessEvent() twice and we
must have some way to distinguish the first call from the second one.

Added a test case verifying that the menu events are indeed processed in the
expected order.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73921 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775