Implement walkthrough state provider

[nzaytsev]

Description

• Map usage tracker data to context to automatically set walkthrough checkboxes
• Adds progress line and badge to home view

The feature is disabled. To enable use setting flag gitlens.test.newWalkthrough

Checklist

• I have followed the guidelines in the Contributing document
• My changes follow the coding style of this project
• My changes build without any errors or warnings
• My changes have been formatted and linted
• My changes include any required corresponding changes to the documentation (including CHANGELOG.md and README.md)
• My changes have been rebased and squashed to the minimal number (typically 1) of relevant commits
• My changes have a descriptive commit message with a short title, including a Fixes $XXX - or Closes #XXX - prefix to auto-close the issue that your PR addresses

[d13]

I think the approach context-key overall looks ok, but I think we can probably simplify WalkthroughStateProvider some. I've left some overall comments to take a look at.

NOTE: I spent a bit of time to re-enable a lot of feature changes to review this locally. Let's not do that in the future.

[d13]

Objects already have strong typing based on the object's shape, so this shouldn't be needed.

[nzaytsev]

Native Object.entries typing doen't work correctly with constant/enum keys, it always considers that keys are strings

[nzaytsev]

Here is an example

In this place it's important to me to know the correct key type. As an alternative I can add a simple assertion like

Object.entries(this.walkthroughByTracking).forEach(
			(entry) => {
				const [usageKey, walkthroughKey] = entry as [TrackedUsageKeys, WalkthroughContextKeys]
			},
		);

[d13]

This worked fine for me:

(Object.entries(this.walkthroughByTracking) as [TrackedUsageKeys, WalkthroughContextKeys][])

[d13]

I don't see rocket-filled used anywhere

[nzaytsev]

I'll use it instead of $(rocket)