add progress signal for progress service and progress indicator

[meganrogge]

note that this is very much a WIP 🚧 and I want some feedback on it early bc I will be OOF starting Friday.

Progress bars around the workbench/editor aren't reported to screen readers ATM despite us doing the right thing to make that happen on the progress bar. #209661 (comment)

Therefore, this PR refactors the chat accessibility signal scheduler that we use for chat response pending into AccessibilityProgressSignalScheduler, which is used by the ProgressService (workbench components) and ProgressIndicator (editors).

I am not sure how necessary this is as most of our progress starts and finishes pretty quickly, meaning this won't typically play with a delay of 1 second and a looping time of 3 seconds. We could of course change those, but I don't want it to be noisy. #209661 (comment)

This does not address the notebook progress signal request because that has its own custom implementation using a progress bar cc @amunger and @rebornix.

I considered implementing this in the progress bar file, so this would also capture notebook progress, but that has layer issues and also is more UI than model.

I would like your feedback @bpasero and @isidorn on this 🙏🏼 and whether or not you think we should have this.

[bpasero]

Should we work on getting this into the base progress bar if that is the best fix? Yes, there is a layer problem, but we have ways around it. For example, the hover work Ben has been doing also hit layer issues and we pragmatically solved it by letting the workbench component set a helper into base:

vscode/src/vs/base/browser/ui/hover/hoverDelegateFactory.ts

Lines 20 to 22 in 180b5b6

	export function setHoverDelegateFactory(hoverDelegateProvider: ((placement: 'mouse' | 'element', enableInstantHover: boolean) => IScopedHoverDelegate)): void {
	hoverDelegateFactory = hoverDelegateProvider;
	}

from

vscode/src/vs/workbench/browser/workbench.ts

Line 163 in 180b5b6

setHoverDelegateFactory((placement, enableInstantHover) => instantiationService.createInstance(WorkbenchHoverDelegate, placement, enableInstantHover, {}));

I also think for alerts, we do something similar for ARIA alerting:

vscode/src/vs/workbench/browser/workbench.ts

Lines 330 to 331 in 180b5b6

	// ARIA
	setARIAContainer(this.mainContainer);

So I am not opposed to having another thing we set into the base progress bar to participate in progress globally and report it via alerts. maybe it could be combined with the existing ARIA thing we have.

[meganrogge]

Sounds good, I'll do something similar. It will still very rarely play AFAICT since we will set the delay to 3 seconds. #209661 (comment)

I have moved part of this to #210582 to make this PR simpler. Edit: going to start from scratch.