change enum MarshalJSON() method to not be called on ptr

[gngrchrl]

We have a bug in the current enum rendering system where the MarshalJSON method is never called on pointer structs. This fixes this behavior (quiet easily).

import (
	"encoding/json"
	"fmt"
)

type Enum struct {
	value string
}

type Enum2 struct {
	valie string
}

func (e Enum) MarshalJSON() ([]byte, error) {
	return []byte("\"another_value\""), nil
}

func (e *Enum2) MarshalJSON() ([]byte, error) {
	return []byte("\"another_value\""), nil
}

type Test struct {
	A Enum
	C Enum2
	B int
}

func main() {
	x := Test{
		A: Enum{},
		C: Enum2{},
		B: 1,
	}
	j, err := json.Marshal(x)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(j))
}

Prints:

{"A":"another_value","C":{},"B":1}

Go playground example: https://go.dev/play/p/8QQzFwO9a-K