Rust: Add SatisfiesConstraintInput module in shared type inference

[paldepind]

This PR refactors the shared type inference library, it untangles the logic for figuring out whether a type tree implements a trait, such that we can expose that logic from the shared library. This is done by a new module called SatisfiesConstraintInput. This module can be used to figure out if and how the type of an AST nodes (or more generally any HasTypeTree) implements a given trait.

---

I believe we can use this module for quite a few things in Rust:

• In for loops like for i of e { ... } where the type of i depends on how e implements the IntoIterator trait.
• Method resolution for trait implementations on type parameters. For an implementation like

  impl<T: Trait1> Trait2 for T { fn a_method(...) ... }

  and a method call like

  receiver.a_method()

  we need to figure out if and how receiver implements Trait1.
• For implicit dereferences through the Deref trait we need to figure out whether the potentially deref'ed value implements Deref.
• If we want to handle calls to closures we must figure out if the target of a call implements Fn, FnOnce, etc.
• For foo.await we must know if foo implements Future.

To show that this works, the last item is carried out in this PR (results in a simplification compared to the current implementation that uses the Matching module). for loops should also be pretty easy, but I didn't want to create conflicts with #19754.

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Below is an explanation of how this module can be used in the case of the iterator in a for loop:

First we create a class that satisfies the HasTypeTree signature and which includes nodes that occur as the iterator in a for loop:

final class ForLoopTarget extends Expr {
  ForLoopTarget() { this = any(ForExpr fe).getIterable() }

  Type getTypeAt(TypePath path) { result = inferType(this, path) }
}

Then we create a modules that satisfies the SatisfiesConstraint signature. The signature only contains a predicate that for every type tree gives the traits that we're interested in that type tree satisfying:

private module SatisfiesConstraintInput implements SatisfiesConstraintSig<ForLoopTarget> {
  predicate relevantConstraint(ForLoopTarget flt, Type constraint) {
    exists(flt) and
    constraint.(TraitType).getTrait() instanceof IntoIteratorTrait
  }
}

Now we can instantiate the module and get the type of e as an implementation of the IntoIterator trait:

SatisfiesConstraint<ForLoopTarget, SatisfiesConstraintInput>::satisfiesConstraintTypeMention(flt,
    constraint, path, t)

This should make it possible to type for loops over any iterator type, which we could do following #19754.

[paldepind]

CI failure is unrelated.

[hvitved]

Very nice refactor.

[hvitved]

I have started a new DCA run.

[paldepind]

Thanks for the comments and thanks for starting DCA :)

[hvitved]

Latest DCA shows that the performance issue was fixed; merging.