Reuse markdown instance for preferences widget

[msujew]

What it does

Closes #12789

The current implementation creates a new instance of markdownit for every preference leaf node. This is quite costly in frontend memory. The change moves the markdownit instance to a dedicated service that is shared across all nodes in a preference model.

In my tests, this reduces the memory consumption of the preference widget by ~165MB:

Before (267MB):

After (102MB):

How to test

1. Open the preference widget.
2. Assert that the memory consumption has been reduced.

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

[kittaakos]

Hello, thanks for the fix. Here, the idea was to reuse the markdown rendering logic from monaco and remove markdown-it. Was it rejected?

[msujew]

@kittaakos I'm not sure how reusable the MarkdownRenderer or MonacoMarkdownRenderer actually are for the purposes of rendering preferences. Especially since we need a renderInline (i.e. no <p> HTML element wrapper) method for the preferences.

[kittaakos]

I'm not sure how reusable the MarkdownRenderer or MonacoMarkdownRenderer actually are for the purposes of rendering preferences.

All clear, thank you!

this reduces the memory consumption of the preference widget by ~165MB:

Awesome contribution

[vince-fugnitto]

LGTM 👍

• confirmed the rendering is correct
• confirmed the memory is significantly improved

[TotooriaHyperion]

Wow, finding my IDE based on 1.39.0 consumes too much memory.
Upgrading to 1.45.1 reduces welcome page memory consumption from 15xMB->7xMB, more than half of it.