vim-patch:9.1.1340: cannot complete :filetype arguments (#33602)

Problem:  cannot complete :filetype arguments (Phạm Bình An)
Solution: add :filetype ex command completion, add "filetypecmd"
          completion type for getcompletion()

fixes: vim/vim#17165
closes: vim/vim#17167

a3422aa317

Co-authored-by: Christian Brabandt <cb@256bit.org>

src/nvim/cmdexpand_defs.h

@@ -108,6 +108,7 @@ enum {
   EXPAND_DIRS_IN_CDPATH,
   EXPAND_SHELLCMDLINE,
   EXPAND_FINDFUNC,
+  EXPAND_FILETYPECMD,
   EXPAND_CHECKHEALTH,
   EXPAND_LUA,
 };