encoding/json: get rid of the stream_test.go TODOs
TestRawMessage now passes without the need for the RawMessage field to
be a pointer. The TODO dates all the way back to 2010, so I presume the
issue has since been fixed.
TestNullRawMessage tested the decoding of a JSON null into a
*RawMessage. The existing behavior was correct, but for the sake of
completeness a non-pointer RawMessage field has been added too. The
non-pointer field behaves differently, as one can read in the docs:
To unmarshal JSON into a value implementing the Unmarshaler
interface, Unmarshal calls that value's UnmarshalJSON method,
including when the input is a JSON null.