THRIFT-4392 reorder structs in plugin.thrift

This fixes #1417
This closes #1413
diff --git a/compiler/cpp/src/thrift/plugin/plugin.thrift b/compiler/cpp/src/thrift/plugin/plugin.thrift
index a93873d..1e51310 100644
--- a/compiler/cpp/src/thrift/plugin/plugin.thrift
+++ b/compiler/cpp/src/thrift/plugin/plugin.thrift
@@ -120,12 +120,6 @@
   3: required t_const_value value
   100: optional string doc
 }
-struct t_struct {
-  1: required TypeMetadata metadata
-  2: required list<t_field> members
-  3: required bool is_union
-  4: required bool is_xception
-}
 struct t_field {
   1: required string name
   2: required t_type_id type
@@ -136,6 +130,12 @@
   99: optional map<string, string> annotations
   100: optional string doc
 }
+struct t_struct {
+  1: required TypeMetadata metadata
+  2: required list<t_field> members
+  3: required bool is_union
+  4: required bool is_xception
+}
 struct t_function {
   1: required string name
   2: required t_type_id returntype