Make wxEventLoop::AddSourceForFD() static.

Make wxEventLoop::AddSourceForFD() static.

Any event sources should be registered with all the event loops, including the
ones that will be started in the future, and not only the current (and
potentially not even existing yet) one. So make AddSourceForFD() method static.

To still allow it to do different things in console and GUI applications, as
it must, virtualize it via the new wxEventLoopSourcesManager class which has
different implementations in the two cases, returned via wxAppTraits as usual.

Notice that this required moving the implementation of this method from
src/osx/core/evtloop_cf.cpp to src/osx/core/utilsexc_cf.cpp as the former file
is base-only and didn't have access to wxGUIAppTraits.

See #10258.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74341 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775