Support proto2 groups

packages/protobuf-bench/README.md

@@ -10,5 +10,5 @@ server would usually do.
 
 | code generator      | bundle size             | minified               | compressed         |
 |---------------------|------------------------:|-----------------------:|-------------------:|
-| protobuf-es         | 90,449 b      | 38,193 b | 9,801 b |
+| protobuf-es         | 91,410 b      | 38,462 b | 9,870 b |
 | protobuf-javascript | 394,384 b  | 288,654 b | 45,122 b |

packages/protobuf-test/extra/proto2.proto

@@ -74,4 +74,23 @@ enum Proto2Enum {
 
 message Proto2ChildMessage {
   optional string string_field = 1;
-}
+}
+
+message Proto2GroupsMessage {
+  optional group Group = 1 {
+    optional int32 int32_field = 1;
+    optional group NestedGroup = 2 {
+      optional string string_field = 1;
+    }
+  }
+  repeated group RepeatedGroup = 2 {
+    optional int32 int32_field = 1;
+  }
+  oneof oneof_with_group {
+    group OneofGroup = 3 {
+      optional bool bool_field = 1;
+    }
+  }
+  optional Group message_field_using_group = 4;
+  optional Group.NestedGroup message_field_using_nested_group = 5;
+}