Simplify markdown rendering for preferences

[msujew]

What it does

Instead of using a custom MarkdownRenderer (introduced with #10431), we simplify the code by correctly using the markdownit library.

How to test

The same testing steps as in #10431, confirm that no regression has occurred.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[msujew]

cc @colin-grant-work You were right, there was a simpler way of handling things. I removed the MarkdownRenderer class. Hopefully, not too many downstream-users started depending on it.

[colin-grant-work]

This approach is leaner than the previous one, and I observe no regressions:

• Clicking on a preference name scrolls that preference into view
• Clicking on a link opens the link in a new browser window.

[msujew]

@colin-grant-work FYI, added the removal of the MarkdownRenderer as a breaking change to the changelog. Will merge after CI is green.

[kittaakos]

@msujew, I have noted that multiple markdown-it instances are used in the preference editor. markdow-it will require linkify-it, which will have the following regex for each preference value. Could Theia (re)use one markdown-it instance for parsing the markdown? With TheiaBlueprint Version 1.32.0 (1.32.0.92), I have dozens of the same regex string. Thank you!

linkify-it.mp4

[colin-grant-work]

With the addition of markdown rendering in the Monaco package, I think it should be possible to get rid of markdown-it entirely in preferences?