Make Marshal(RawMessage) behave like encoding/json

[greensea]

In encoding/json, there is MarshalJSON() and UnmarshaslJSON() for RawMessage. Missing this two method leads to different behavior while Marshal() jsoniter.RawMessage using std json package.

Example code below

package main import ( "fmt" "encoding/json" "github.com/json-iterator/go" ) type T struct { Msg jsoniter.RawMessage } func main() { var j T raw := []byte(`{ "Msg": {"Foo": "Bar"}}`) jsoniter.Unmarshal(raw, &j) b1, _ := json.Marshal(j.Msg) fmt.Printf("%s\n", b1) /// Expect `{"Foo": "Bar"}` but got `"IHsiRm9vIjogIkJhciJ9"` b2, _ := jsoniter.Marshal(j.Msg) fmt.Printf("%s\n", b2) } 

[codecov]

Codecov Report

Merging #474 into master will decrease coverage by 0.50%.
The diff coverage is 22.22%.

@@ Coverage Diff @@ ## master #474 +/- ## ========================================== - Coverage 86.64% 86.14% -0.51%  ========================================== Files 41 41 Lines 5100 5109 +9 ========================================== - Hits 4419 4401 -18  - Misses 540 566 +26  - Partials 141 142 +1 

Impacted Files	Coverage Δ
adapter.go	81.15% <22.22%> (-8.85%)	⬇️
reflect_struct_decoder.go	82.68% <0.00%> (-2.67%)	⬇️

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