Replace Path.toString() with fsPath()

[msujew]

What it does

Closes #10830

Simply does as the commit says. Since we often display file system paths to the user, formatting them in the style of the backend operating system is often preferable. That's what Path.fsPath() does.

How to test

You will need a Windows system to test the improved behavior.

Assert that the paths displayed in tooltips, messages, etc. are correctly formatted for the actual backend system:

• Search in workspace view
• Editor tabs
• Open Editors view
• Navigator view
• Problem view
• Preferences (such as the Windows Exec with its browse functionality)
• Property view (for files)

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

[colin-grant-work]

I don't observe any regressions, and the inter-platform functionality works nicely. 👍