Optimize showing recent workspaces

[msujew]

What it does

I've recently noticed that attempting to execute the "Open recent workspace" command takes a few seconds on Windows. This change optimizes quite a lot of the old code to improve the performance and also fix a few issues regarding incorrectly displayed paths. In order to get the most performance out of it, I had to remove the pretty expensive FileService#resolve calls which were used to differentiate between file and directory workspaces.

How to test

1. Run the "Open recent workspace" command.
2. Assert that it effectively instantly opens the quick pick for the workspaces
3. Assert that there are no regressions.

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