Exclude windows not accepting keyboard focus from GTK focus chain.

Exclude windows not accepting keyboard focus from GTK focus chain.

For some reason the test for AcceptsFocusFromKeyboard() wasn't done in the
correct place when constructing the GTK focus chain and even windows returning
false from it were still added to it.

Do not do this any more, this prevents the windows which are really not meant
to be focusable from keyboard (such as the pseudo-buttons in the generic
implementation of wxSearchCtrl) from gaining focus unexpectedly.

See #12808.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68367 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775