Support state stream API

[jribbink]

Problem

The emulator does not currently implement the state stream API needed for events streaming

Steps to Reproduce

Try using events streaming (i.e. ws://localhost:8888/v1/subscribe_events) and the endpoint will not be available because the state_stream.API instance used to instantiate the REST server is nil

flow-emulator/server/access/rest.go

Lines 99 to 117 in 0cdc31c

	srv, err := rest.NewServer(
	adapter,
	rest.Config{
	ListenAddress: fmt.Sprintf("%s:3333", host),
	WriteTimeout: rest.DefaultWriteTimeout,
	ReadTimeout: rest.DefaultReadTimeout,
	IdleTimeout: rest.DefaultIdleTimeout,
	},
	debugLogger,
	chain,
	restCollector,
	nil,
	backend.Config{
	EventFilterConfig: state_stream.DefaultEventFilterConfig,
	ClientSendTimeout: state_stream.DefaultSendTimeout,
	ClientSendBufferSize: state_stream.DefaultSendBufferSize,
	MaxGlobalStreams: state_stream.DefaultMaxGlobalStreams,
	HeartbeatInterval: state_stream.DefaultHeartbeatInterval,
	},

Acceptance Criteria

Event streaming supported by emulator

Context

Blocking adoption of event streaming API (i.e. onflow/fcl-js#1791)