Fix 'clientId' is undefined for RealtimeMessage

`clientId` prop was made optional in ably-js v2 [1] to be consistent
with the feature spec. However, spaces SDK requires `clientId` to be
always set, so we can expect it to be present.

[1] ably/ably-js@4e3733f

Author: VeskeR

src/CursorDispensing.ts

@@ -36,7 +36,7 @@ export default class CursorDispensing {
     const updates: { cursor: CursorUpdate; offset: number }[] = message.data || [];
 
     updates.forEach((update: { cursor: CursorUpdate; offset: number }) => {
-      const enhancedMsg = {
+      const enhancedMsg: { cursor: CursorUpdate; offset: number } = {
         cursor: {
           clientId: message.clientId,
           connectionId: message.connectionId,

src/utilities/types.ts

@@ -28,6 +28,7 @@ export type Subset<T> = {
   [attr in keyof T]?: T[attr] extends object ? Subset<T[attr]> : T[attr];
 };
 
-export type RealtimeInboundMessage = Omit<InboundMessage, 'connectionId'> & {
+export type RealtimeInboundMessage = Omit<InboundMessage, 'clientId' | 'connectionId'> & {
+  clientId: string;
   connectionId: string;
 };