Rust: Fix type inference for trait objects for traits with associated types

[paldepind]

This PR adds tests that shows two problems:

• For a subtrait of a supertrait with associated types, we don't handle the associated type for correctly for the subtrait.
• For a dyn Trait type we don't handle any associated types that Trait might have.

I stumbled into both of these issues while trying to implement type inference for closures since the traits for functions (Fn, FnOnce, FnMut) use associated types.

This PR also fixes the second issue which is done by letting dyn Trait have matching type parameters for the associated types of Trait similar to what is done for the normal type parameters.

[Copilot]

Pull Request Overview

This PR fixes type inference for trait objects (dyn Trait) when traits have associated types, specifically addressing two issues: handling associated types for subtraits of supertraits with associated types, and properly handling associated types in dyn Trait types. The fix involves extending the type parameter system to include both generic type parameters and associated type parameters for trait objects.

• Refactors the DynTraitTypeParameter class to handle both TypeParam and TypeAlias nodes
• Adds comprehensive test coverage for associated types in trait objects and supertrait scenarios
• Updates type mention resolution logic to properly handle the new type parameter structure

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rust/ql/test/library-tests/type-inference/main.rs	Adds test module for supertrait associated types and renames existing module
rust/ql/test/library-tests/type-inference/dyn_type.rs	Adds comprehensive tests for trait objects with associated types
rust/ql/test/library-tests/type-inference/CONSISTENCY/PathResolutionConsistency.expected	Updates line numbers in consistency test expectations
rust/ql/lib/codeql/rust/internal/TypeMention.qll	Updates type resolution logic for dyn trait type parameters
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Extends type parameter ID generation to handle associated types
rust/ql/lib/codeql/rust/internal/Type.qll	Major refactor of DynTraitTypeParameter to support both generic and associated type parameters

Comments suppressed due to low confidence (1)

rust/ql/lib/codeql/rust/internal/Type.qll:438

• [nitpick] The method name toStringInner is ambiguous. Consider renaming it to getNodeDisplayName or formatNodeName to better indicate its purpose of formatting the underlying node for display.

  private string toStringInner() {

[geoffw0]

Looks good, couple of minor suggestions.

[geoffw0]

.(AstNode) appears to be redundant.

[paldepind]

This is to help QL figure out what the element type of the set is. It complains without the .(AstNode) :)

[geoffw0]

That's surprising, but fair enough.