Ensure that key events are sent to focused window first in wxGTK.

Ensure that key events are sent to focused window first in wxGTK.

Start processing key events from the currently focused window, this ensures
that its key event handlers are tried before the top level window
accelerators.

This is consistent with wxMSW and allows a window to locally override the
global accelerators which really makes sense.

Closes #14553.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72640 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775