Addressing instance methods in external annotations

[JustusAdam]

What Changed?

This PR expands the capabilities of the resolution code used for external markers and the --analyze command line argument to handle more complex Rust paths, such as <Type as Trait>::method.

We reuse rustcs own parser to interpret the user-supplied string as a "path".

Why Does It Need To?

Currently external markers and the --analyze command line argument are limited to simple paths (e.g. std::vec::Vec) and cannot target methods of a trait impl. This PR removes that limitation.

Checklist

• Need to handle generics on the self-ty in the qualified case or at least error.
• Need to handle the qualified case without a trait
• Need to re-enable otype annotation.
• Above description has been filled out so that upon quash merge we have a
  good record of what changed.
• New functions, methods, types are documented. Old documentation is updated
  if necessary
• Documentation in Notion has been updated
• Tests for new behaviors are provided
  • New test suites (if any) ave been added to the CI tests (in
    .github/workflows/rust.yml) either as compiler test or integration test.
    Or justification for their omission from CI has been provided in this PR
    description.