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/block.go

@@ -334,7 +334,7 @@ type Header struct {
 	// basic block info
 	Version version.Consensus `json:"version"`
 	ChainID string            `json:"chain_id"`
-	Height  int64             `json:"height"`
+	Height  int64             `json:"height,string"`
 	Time    time.Time         `json:"time"`
 
 	// prev block info
@@ -748,7 +748,7 @@ type Commit struct {
 	// ValidatorSet order.
 	// Any peer with a block can gossip signatures by index with a peer without
 	// recalculating the active ValidatorSet.
-	Height     int64       `json:"height"`
+	Height     int64       `json:"height,string"`
 	Round      int32       `json:"round"`
 	BlockID    BlockID     `json:"block_id"`
 	Signatures []CommitSig `json:"signatures"`