show call stacks more friendly

[robberphex]

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While debugging, the call stack panel list all of the threads:

But most of the threads are not related to the application; they are just builtin threads(Finalizer, most of http-nio-808-exec-*). So, why not just put threads into a drop-down box? When I select the current thread, show call stack of the current thread, and the UI will be more efficient:

[testforstephen]

This is involved with the vscode experience, oops. I'd suggest to move it to vscode repository for further discussion.