Implement workbench.editor.revealIfOpen preference

[colin-grant-work]

What it does

Implements the workbench.editor.revealIfOpen preference.

How to test

1. By default the preference should be false. That means that if you open a file, it should by default open on the active tabbar even if you already have an editor open for that file on another tabbar.
2. If you set the preference to true, an existing editor for a file should be revealed if it is present, even if it is present on another tab than the current active tab.

Note that it should be revealed; it may not be focused, so if you e.g. click from the explorer to open the file, the explorer may remain focused unless you double click. That appears to be consistent with VCode's behavior, though I'm open to defaulting to activating in that case.

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]

LGTM 👍

• if the preference is false the editor will open in the active tabbar if it can
• if the preference is true the editor will be revealed if it is already open in a tabbar