Support determinate progress indicators

[AlexTugarev]

Currently only indeterminate progress indicators are rendered at locations like SCM/GIT, Search, and Debug.

@westbury suggested to support rendering progress based on the known percentage in #6009 (comment)

While there are places like SCM were we expect to aggregate the process indication of concurrent tasks, which is hard to do with a determinate progress bar, there are certainly use cases where the process in percent would be interesting. As stated in #6009 (comment), this is support in the reporter site already (see ProgressService,) but ignored on the renderer site as of now.

It's feasible to change the behavior to render a progress bar based on the progress update, if it's provided and it's possible to aggregate. Which especially means, if there is a single task which does report progress updates, the rendering mode should be determinate progress, and in some other cases it would be indeterminate progress.