Use OpenService to handle preferences

[msujew]

What it does

Closes #10806

Refactors some code from PreferenceNodeRenderer into its own OpenHandler. This way we can target the OpenService purely instead of relying on some adhoc implementation. Also allows to open preferences from outside the preferences widget (VSCode does that a lot).

How to test

1. Confirm that links/references to other preferences still work as expected.
2. Download and install this sample extension.
3. Search for hello command in the preference widget.
4. Click on the link, a notification with Hello World! should appear.

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

[vince-fugnitto]

The changes look good to me, and work well 👍

• confirmed that commands contributed by plugins work well
• confirmed that internal links work well (jumps to corresponding preference)
• confirmed that external links (ex: documentation) work well

cc @colin-grant-work any concerns?

[colin-grant-work]

Looks good to me. Neat, though I suspect no accident, that the internal preference links were already formatted to make this easy. 👍

[vince-fugnitto]

Confirming approval :)