Support indeterminate progress notifications in message service

[planger]

Clients can report progress via the message service, which then would show up as follows:

However, also as can be seen in the first notification state "Doing something", the notification doesn't show any progress indication if there is no work progress being specified. Thus, the notification can't be distinguished from plain info notifications. However, reporting progress with indeterminate progress is often useful, e.g. when dealing with external processes.

Feature Description:

I suggest to show an indeterminate progress indication if clients report progress without specifying a work progress. This is also in line with VS Code, which shows an indeterminate progress indicator if clients don't specify progress.

The following should show indeterminate progress:

this.messageService
    .showProgress({
        text: 'Starting to report indeterminate progress',
    })
    .then(progress => {
        // do something
        progress.report({
            message: 'First step completed',
        });
        // do something
        progress.report({
            message: 'Next step completed',
        });
        // do something
        progress.report({
            message: 'Complete',
        });
        // do something
        progress.cancel();
    });

And the following should report actual progress:

this.messageService
    .showProgress({
        text: 'Starting to report progress',
    })
    .then(progress => {
        // do something
        progress.report({
            message: 'First step completed',
            work: { done: 25, total: 100 }
        });
        // do something
        progress.report({
            message: 'Next step completed',
            work: { done: 60, total: 100 }
        });
        // do something
        progress.report({
            message: 'Complete',
            work: { done: 100, total: 100 }
        });
        // do something
        progress.cancel();
    });

[planger]

I'll submit a PR for that soon.