Add wxT_2() macro for compatibility with wxWidgets 2 API.

This macro can be used to make the same code compile with both v2 and v3 as it
expands to wxT() in 2.8 and nothing in later versions.

See #12925.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66968 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/chartype.h

@@ -250,6 +250,12 @@
     #endif /* ASCII/Unicode */
 #endif /* !defined(wxT) */
 
+/*
+    wxT_2 exists only for compatibility with wx 2.x and is the same as wxT() in
+    that version but nothing in the newer ones.
+ */
+#define wxT_2(x) x
+
 /*
    wxS ("wx string") macro can be used to create literals using the same
    representation as wxString does internally, i.e. wchar_t in Unicode build