Rust: Infer certain type for shorthand self

[paldepind]

We currently infer certain type information for self in fn f(self: Self) but not for self in fn f(self) even though the latter is just syntactic sugar for the former. This PR removes that distinction. Just in our tests, that removes 4 spurious types.

The PR uses the word "shorthand" which comes from the Rust reference which uses the terms "shorthand self" and "shorthand syntax".

The logic for inferring the type of a shorthand self parameters is now included inside inferAnnotatedType which I think makes sense as there's explicit annotations right beneath the sugar.

The first DCA run showed a performance regression that I can't reproduce locally (I tried quick evaling inferType on iced). The second DCA run shows only a tiny performance regression, and doesn't really agree with the first. For instance, neon-empty-diff was the biggest regression in the first run but shows a speedup in the second. So I think it's just noice, and the rest of the DCA report looks as expected.

[Copilot]

Pull Request Overview

This PR improves type inference for Rust's shorthand self parameters by treating them consistently with explicit self: Self annotations. The change extends type inference to cover implicit self parameter syntax, which is syntactic sugar for explicit self type annotations.

Key changes:

• Unifies type inference logic for both shorthand and explicit self parameter syntax
• Moves shorthand self type inference into the inferAnnotatedType function
• Removes duplicate logic for implicit self parameter handling

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
rust/ql/test/library-tests/type-inference/type-inference.expected	Test expectations updated to reflect removal of spurious type inferences
rust/ql/test/library-tests/type-inference/main.rs	Added certainType annotations to test shorthand self parameters
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Refactored self parameter type inference logic and consolidated duplicate functions