patch 8.2.3967: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/highlight.c b/src/highlight.c
index c4f5c66..7349f4b 100644
--- a/src/highlight.c
+++ b/src/highlight.c
@@ -4273,7 +4273,7 @@
 
     if (di->di_tv.v_type != VAR_STRING || di->di_tv.vval.v_string == NULL)
     {
-	emsg(_(e_stringreq));
+	emsg(_(e_string_required));
 	*error = TRUE;
 	return NULL;
     }
@@ -4306,7 +4306,7 @@
 
     if (di->di_tv.v_type != VAR_DICT || di->di_tv.vval.v_dict == NULL)
     {
-	emsg(_(e_dictreq));
+	emsg(_(e_dictionary_required));
 	return FALSE;
     }
 
@@ -4548,7 +4548,7 @@
     {
 	if (li->li_tv.v_type != VAR_DICT)
 	{
-	    emsg(_(e_dictreq));
+	    emsg(_(e_dictionary_required));
 	    return;
 	}