fix: Allow trait method references from the trait name

[jfecher]

Description

Problem*

Resolves #3773
Part of #2568

Summary*

This PR implements the ability to be able to call trait methods such as Default::default() where previously we required StructName::default(). The specific impl is selected via type inference. Previously, this resulted in a compiler panic.

Additional Context

When a trait method's type isn't constrained enough or is otherwise still ambiguous after type inference, the compiler currently just selects the first trait implementation that matches. E.g. let _ = Default::default();. This is a separate issue, so I'll create a new issue for this.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.
  • I think traits are finally stable enough to start writing documentation for. I'm going to submit another PR to remove some of the experimental warnings the compiler has for traits, and with it add documentation for traits as well. This wouldn't stabilize all trait features (e.g. associated types are still unimplemented), but users will now be able to use basic traits with functions without warnings. Any unimplemented trait items (associated types again) will not be included in the documentation.

PR Checklist*

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

[jfecher]

This PR is now ready for review

[jfecher]

Frontend tests should be fixed now. Something odd is going on in them - they have unused variable warnings and one duplicated error. Neither of which occur when running nargo execute on the same source program.