vim-patch:9.1.0010: Keymap completion is not available (#26888)

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: vim/vim#13692

81642d9d6f

Co-authored-by: Doug Kearns <dougkearns@gmail.com>

src/nvim/cmdexpand_defs.h

@@ -105,6 +105,7 @@ enum {
   EXPAND_STRING_SETTING,
   EXPAND_SETTING_SUBTRACT,
   EXPAND_ARGOPT,
+  EXPAND_KEYMAP,
   EXPAND_CHECKHEALTH,
   EXPAND_LUA,
 };