Add minor fixes and performance improvements on channel switch (#6469)

* Add minor fixes and performance improvements

* Add comment

app/hooks/channel_switch.ts

@@ -0,0 +1,33 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {useEffect, useState} from 'react';
+import {DeviceEventEmitter} from 'react-native';
+
+import {Events} from '@constants';
+
+export const useChannelSwitch = () => {
+    const [loading, setLoading] = useState(false);
+    useEffect(() => {
+        let time: NodeJS.Timeout | undefined;
+        const l = DeviceEventEmitter.addListener(Events.CHANNEL_SWITCH, (switching: boolean) => {
+            if (time) {
+                clearTimeout(time);
+            }
+            if (switching) {
+                setLoading(true);
+            } else {
+                // eslint-disable-next-line max-nested-callbacks
+                time = setTimeout(() => setLoading(false), 0);
+            }
+        });
+        return () => {
+            l.remove();
+            if (time) {
+                clearTimeout(time);
+            }
+        };
+    }, []);
+
+    return loading;
+};