MM-56071: Track multiple threads (#25775)

We can have 2 types of threads open at the same time. One from
the thread view, and another from RHS.

We add another variable to distinguish between the 2 states.

In future, if we have the ability for more than 2 threads, then
we would need to track by threadID.

https://mattermost.atlassian.net/browse/MM-56071

```release-note
NONE
```

webapp/channels/src/components/threading/thread_viewer/thread_viewer.test.tsx

@@ -67,6 +67,7 @@ describe('components/threading/ThreadViewer', () => {
         postIds: [post.id],
         appsEnabled: true,
         rootPostId: post.id,
+        isThreadView: true,
     };
 
     test('should match snapshot', async () => {

webapp/channels/src/components/threading/thread_viewer/thread_viewer.tsx

@@ -49,7 +49,7 @@ export type Props = Attrs & {
     postIds: string[];
     highlightedPostId?: Post['id'];
     selectedPostFocusedAt?: number;
-    isThreadView?: boolean;
+    isThreadView: boolean;
     inputPlaceholder?: string;
     rootPostId: string;
     fromSuppressed?: boolean;
@@ -81,7 +81,7 @@ export default class ThreadViewer extends React.PureComponent<Props, State> {
     }
 
     public componentWillUnmount() {
-        WebSocketClient.updateActiveThread('');
+        WebSocketClient.updateActiveThread(this.props.isThreadView, '');
     }
 
     public componentDidUpdate(prevProps: Props) {
@@ -184,7 +184,7 @@ export default class ThreadViewer extends React.PureComponent<Props, State> {
         }
 
         if (this.props.channel) {
-            WebSocketClient.updateActiveThread(this.props.channel?.id);
+            WebSocketClient.updateActiveThread(this.props.isThreadView, this.props.channel?.id);
         }
         this.setState({isLoading: false});
     };