patch 8.2.3226: new digraph functions use old naming scheme

Problem:    New digraph functions use old naming scheme.
Solution:   Use the digraph_ prefix. (Hirohito Higashi, closes #8580)
diff --git a/src/edit.c b/src/edit.c
index 96464de..267c76d 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -5219,7 +5219,7 @@
 	if (cc != ESC)
 	{
 	    AppendToRedobuff((char_u *)CTRL_V_STR);
-	    c = getdigraph(c, cc, TRUE);
+	    c = digraph_get(c, cc, TRUE);
 #ifdef FEAT_CMDL_INFO
 	    clear_showcmd();
 #endif