patch 9.1.0010: Keymap completion is not available

Problem:  Keymap completion is not available
Solution: Add keymap completion (Doug Kearns)

Add keymap completion to the 'keymap' option, user commands and builtin
completion functions.

closes: #13692

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/option.c b/src/option.c
index 7cac89e..2372c1a 100644
--- a/src/option.c
+++ b/src/option.c
@@ -7412,6 +7412,13 @@
 	xp->xp_context = EXPAND_FILETYPE;
 	return;
     }
+#ifdef FEAT_KEYMAP
+    if (options[opt_idx].var == (char_u *)&p_keymap)
+    {
+	xp->xp_context = EXPAND_KEYMAP;
+	return;
+    }
+#endif
 
     // Now pick. If the option has a custom expander, use that. Otherwise, just
     // fill with the existing option value.