patch 9.1.1340: cannot complete :filetype arguments

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

fixes: #17165
closes: #17167

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/vim.h b/src/vim.h
index 41984da..fbe5c34 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -854,6 +854,7 @@
 #define EXPAND_SHELLCMDLINE	60
 #define EXPAND_FINDFUNC		61
 #define EXPAND_HIGHLIGHT_GROUP  62
+#define EXPAND_FILETYPECMD	63
 
 
 // Values for exmode_active (0 is no exmode)