create flag info file in mainline build

Bug: b/301491148
Test: m
Change-Id: I2a0abe215510acb78526b0e1c68b5881af7997fd
diff --git a/apex/builder.go b/apex/builder.go
index 437189f..19ec1bd 100644
--- a/apex/builder.go
+++ b/apex/builder.go
@@ -96,6 +96,7 @@
 	{"package.map", "create_aconfig_package_map_file", "package_map"},
 	{"flag.map", "create_aconfig_flag_map_file", "flag_map"},
 	{"flag.val", "create_aconfig_flag_val_file", "flag_val"},
+	{"flag.info", "create_aconfig_flag_info_file", "flag_info"},
 }
 
 var (