Fix wxSTC compilation without wxUSE_DRAG_AND_DROP after r65827.

Fix wxSTC compilation without wxUSE_DRAG_AND_DROP after r65827.

Correct the changes of r65827 to also compile with wxUSE_DRAG_AND_DROP==0
(especially important for the ports without dnd support such as wxX11 and
wxDFB).

Also do the changes in the correct files, i.e. src/stc/stc.{h,cpp}.in and not
in the generated files themselves to prevent them from being overwritten the
next time gen_iface.py is ran.

Finally keep backwards compatibility as SetDragAllowMove(bool) is a public
method so preserve its old semantics and add a new SetDragFlags() instead of
silently breaking the existing code using SetDragAllowMove().

See #11709.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65840 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775