patch 8.2.4398: some command completion functions are too long

Problem:    Some command completion functions are too long.
Solution:   Refactor code into separate functions.  Add a few more tests.
            (Yegappan Lakshmanan, closes #9785)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4398,
 /**/
     4397,
 /**/