patch 8.2.2452: no completion for the 'filetype' option

Problem:    No completion for the 'filetype' option.
Solution:   Add filetype completion. (Martin Tournoij, closes #7747)
diff --git a/src/optiondefs.h b/src/optiondefs.h
index 6cea017..9961bd4 100644
--- a/src/optiondefs.h
+++ b/src/optiondefs.h
@@ -946,7 +946,7 @@
 				    (char_u *)FALSE,
 #endif
 					(char_u *)0L} SCTX_INIT},
-    {"filetype",    "ft",   P_STRING|P_ALLOCED|P_VI_DEF|P_NOGLOB|P_NFNAME,
+    {"filetype",    "ft",   P_STRING|P_EXPAND|P_ALLOCED|P_VI_DEF|P_NOGLOB|P_NFNAME,
 			    (char_u *)&p_ft, PV_FT,
 			    {(char_u *)"", (char_u *)0L}
 			    SCTX_INIT},