Fix non-ASCII msgids with wxGETTEXT_IN_CONTEXT_PLURAL

The compilation fix in PR wxWidgets#24925 aimed for the
wxNO_IMPLICIT_WXSTRING_ENCODING case presumably also has the
side effect of preventing non-ASCII (non-English) msgids with
wxGETTEXT_IN_CONTEXT_PLURAL, also in the regular case when
implicit encoding is permitted.

It is best to define wxGETTEXT_IN_CONTEXT_PLURAL separately for
both wxNO_IMPLICIT_WXSTRING_ENCODING and without it, similarly
to how wxGETTEXT_IN_CONTEXT is defined. For some reason it
was defined only once until now.

include/wx/translation.h

@@ -60,12 +60,14 @@ using wxTranslationsHashMap = std::unordered_map<wxString, wxString>;
 #ifndef wxNO_IMPLICIT_WXSTRING_ENCODING
 #define wxGETTEXT_IN_CONTEXT(c, s) \
     wxGetTranslation((s), wxString(), c)
+#define wxGETTEXT_IN_CONTEXT_PLURAL(c, sing, plur, n) \
+    wxGetTranslation((sing), (plur), n, wxString(), c)
 #else
 #define wxGETTEXT_IN_CONTEXT(c, s) \
     wxGetTranslation(wxASCII_STR(s), wxString(), wxASCII_STR(c))
-#endif
 #define wxGETTEXT_IN_CONTEXT_PLURAL(c, sing, plur, n) \
     wxGetTranslation(wxASCII_STR(sing), wxASCII_STR(plur), n, wxString(), wxASCII_STR(c))
+#endif
 
 // another one which just marks the strings for extraction, but doesn't
 // perform the translation (use -kwxTRANSLATE with xgettext!)