Theia: stale progress reporting

[akosyakov]

I've noticed that progress reporting in the explorer runs forever sometimes. During debugging of such cases I see that all progress tasks are properly cleaned up but progress is still rendered.

I think there is a race condition here: https://github.com/eclipse-theia/theia/blob/d0e00c5d07ec0c95a17da51a5b744934d7c4d1f8/packages/core/src/browser/progress-location-service.ts#L68-L76

If several progresses running the last one win cancel out event for previous, so the explorer location never sees done event for instance.

cc @AlexTugarev

[vince-fugnitto]

I noticed it today for the debug view:

If it helps, here are the reproduction steps:

1. open the debug view
2. click the Start Debugging button ('attach by process id' was selected)
3. press esc
4. the progress will be displayed always