output: fix the selected channel name

[inlann]

What it does

Fix the channel selector of the output view toolbar. Let the selector automatically switch to the selected channel name based on the current channel name.

How to test

1. Create a class at the frontend and inject the OutputChannelManager
2. Get a channel using `this.outputChannelManager.getChannel('Test Channel')
3. Show the channel and push some message into it using channel.show() and channel.appendLine('test message', OutputChannelSeverity.Info)
4. The output view will show the message but the channel selector does not switch to the Test Channel.
5. This pull request fixes the channel selector and lets it automatically switch to the selected channel name based on the current channel name.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

Thank you for the contribution 👍
I confirm that the changes work as expected, the toolbar properly updates it's name.