Allow the file system provider to narrow down libraries to library list

[worksofliam]

Changes

Allow the file system provider, when reading the root directories, to only returns libraries that are on the library list. This improves the usability when

How to test this PR

1. Create a .code-workspace file with this content: {"folders": [{"name": "IBM i", "uri": "member:/#libl"}]}
2. Open that workspace, and connect to a system
3. See the library list appear in the Explorer view, where entries can be expanded.

Checklist

• have tested my change
• have created one or more test cases
• updated relevant documentation
• Remove any/all console.logs I added
• have added myself to the contributors' list in CONTRIBUTING.md

[github-actions]

👋 A new build is available for this PR based on 7e0050e.

• Download here.
• Read more about how to test