rpc: simplify the encoding of interface-typed arguments in JSON (#7600)

Add package jsontypes that implements a subset of the custom libs/json 
package. Specifically it handles encoding and decoding of interface types
wrapped in "tagged" JSON objects. It omits the deep reflection on arbitrary
types, preserving only the handling of type tags wrapper encoding.

- Register interface types (Evidence, PubKey, PrivKey) for tagged encoding.
- Update the existing implementations to satisfy the type.
- Register those types with the jsontypes registry.
- Add string tags to 64-bit integer fields where needed.
- Add marshalers to structs that export interface-typed fields.

types/genesis.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/tendermint/tendermint/crypto"
+	"github.com/tendermint/tendermint/internal/jsontypes"
 	tmbytes "github.com/tendermint/tendermint/libs/bytes"
 	tmjson "github.com/tendermint/tendermint/libs/json"
 	tmtime "github.com/tendermint/tendermint/libs/time"
@@ -29,10 +30,23 @@ const (
 type GenesisValidator struct {
 	Address Address       `json:"address"`
 	PubKey  crypto.PubKey `json:"pub_key"`
-	Power   int64         `json:"power"`
+	Power   int64         `json:"power,string"`
 	Name    string        `json:"name"`
 }
 
+func (g GenesisValidator) MarshalJSON() ([]byte, error) {
+	pk, err := jsontypes.Marshal(g.PubKey)
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(struct {
+		Address Address         `json:"address"`
+		PubKey  json.RawMessage `json:"pub_key"`
+		Power   int64           `json:"power,string"`
+		Name    string          `json:"name"`
+	}{Address: g.Address, PubKey: pk, Power: g.Power, Name: g.Name})
+}
+
 // GenesisDoc defines the initial conditions for a tendermint blockchain, in particular its validator set.
 type GenesisDoc struct {
 	GenesisTime     time.Time          `json:"genesis_time"`