Handle json.RawMessage or introduce a similar type

[nieomylnieja]

Is your feature request related to a problem? Please describe.
When decoding models that support both JSON and YAML encoding, it's convenient that we already support json tags for YAML, but when using json.RawMessage go-yaml does not handle it.
Due to that there's no native (from go-yaml perspective) way to handle such models.
Converting from YAML to JSON is not an option for me as I want to retain separate syntax errors for JSON and YAML.

Describe the solution you'd like
We should either handle json.RawMessage type or introduce a new type, like yaml.RawMessage which could implement both json.(Un)marshaler and yaml.Bytes(Un)marshaler interfaces.

Describe alternatives you've considered
Currently I've implemented my own type for that.
Having to redefine it in every project I work with though is not ideal.

package serdeutil

import "github.com/pkg/errors"

// RawMessage is a raw encoded JSON or YAML value.
// It implements:
// - [json.Marshaler] and [json.Unmarshaler]
// - [yaml.BytesMarshaler] and [yaml.BytesUnmarshaler]
// It can be used to delay JSON/YAML decoding or precompute a JSON/YAML encoding.
type RawMessage []byte

func (m RawMessage) MarshalJSON() ([]byte, error) { return m.marshal() }
func (m RawMessage) MarshalYAML() ([]byte, error) { return m.marshal() }

func (m RawMessage) marshal() ([]byte, error) {
	if m == nil {
		return []byte("null"), nil
	}
	return m, nil
}

func (m *RawMessage) UnmarshalJSON(data []byte) error { return m.unmarshal(data) }
func (m *RawMessage) UnmarshalYAML(data []byte) error { return m.unmarshal(data) }

func (m *RawMessage) unmarshal(data []byte) error {
	if m == nil {
		return errors.New("RawMessage: unmarshal on nil pointer")
	}
	*m = append((*m)[0:0], data...)
	return nil
}