Add LiveObjects access and subscription public API to the ably.d.ts

This is barebones public API definitions (missing documentation) to
enable LiveObjects plugin package tests and TypeScript checks.

ably.d.ts

@@ -2028,7 +2028,44 @@ export declare interface PushChannel {
 /**
  * Enables the LiveObjects state to be subscribed to for a channel.
  */
-export declare interface LiveObjects {}
+export declare interface LiveObjects {
+  getRoot(): Promise<LiveMap>;
+}
+
+// TODO: document public API for LiveObjects
+
+export declare interface LiveMap extends LiveObject<LiveMapUpdate> {
+  get(key: string): LiveObject | StateValue | undefined;
+  size(): number;
+}
+
+export declare interface LiveMapUpdate extends LiveObjectUpdate {
+  update: { [keyName: string]: 'updated' | 'removed' };
+}
+
+export type StateValue = string | number | boolean | Buffer | Uint8Array;
+
+export declare interface LiveCounter extends LiveObject<LiveCounterUpdate> {
+  value(): number;
+}
+
+export declare interface LiveCounterUpdate extends LiveObjectUpdate {
+  update: { inc: number };
+}
+
+export declare interface LiveObject<TUpdate extends LiveObjectUpdate = LiveObjectUpdate> {
+  subscribe(listener: (update: TUpdate) => void): SubscribeResponse;
+  unsubscribe(listener: (update: TUpdate) => void): void;
+  unsubscribeAll(): void;
+}
+
+export declare interface LiveObjectUpdate {
+  update: any;
+}
+
+export declare interface SubscribeResponse {
+  unsubscribe(): void;
+}
 
 /**
  * Enables messages to be published and historic messages to be retrieved for a channel.