thrift/lib/thrift/SerializableDynamic.h: fixes for modular builds
thrift/lib/thrift/SerializableDynamic.h: fixes for modular builds

Summary: Add some missing includes and remove conditional on `THRIFT_CPP2_H_`.

Reviewed By: yfeldblum

Differential Revision: D13175869

fbshipit-source-id: c61a3954d039499a2a86986d913c3a9f7d803239

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift