chore: remove path virtualization from FileManager

[TomAFrench]

Description

Problem*

Resolves

Summary*

I'm not sure what the purpose of wrapping PathBufs in VirtualPath was but its main effect is requiring us to reattach the noir file extension in a load of locations after it's stripped off in virtualisation.

This PR removes this layer of abstraction and we now maintain the .nr extension on our paths. This should help prevent broken paths from forgetting to re-add the extension in future.

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[kevaundray]

I think the rationale was so that you could:

• Abstract away any filepath differences with windows and linux
• If you wanted to, you could support files which are not in the filesystem by using the VirtualPath as an unique opaque identifier.

This code has changed significantly since then, so perhaps its fine to just remove it. Either way, if we need the above features, it would be better to re-implement VirtualPath again in the future with more intention.

[TomAFrench]

Yeah, I think that we can reintroduce it later if necessary. It's entirely internal to the fm package anyway.