Refactor preference tree layouting

[msujew]

What it does

Closes #13802
Supersedes #12929

Adds a new PreferenceLayoutProvider service that allows us to translate preference tree items. Also reuses some code from #12929 to correctly display plugin configuration groups in the settings widget.

How to test

1. Start Theia and confirm that the preference tree behaves as in VS Code.
2. Install a language pack and assert that the preference tree is localized.
3. Assert that preferences from the TypeScript extension are displayed as TypeScript and not Typescript and Javascript.

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

[tsmaeder]

If I understand this correctly, the additional NLS is only happening for section titles, not the leaf configuration properties themselves?

[tsmaeder]

I also seems really smelly that the preferences tree knows about preferences for all kinds of Theia extensions (like scm) which may not even be present in a Theia-based product. Are we doing this to simulate the same appearance as VS Code?

[tsmaeder]

Works as advertised, just some comments on the code.