Guards: Refactor EqualityTest interface.

[aschackmull]

A minor refactor in the interface to the Guards library. This is necessary to facilitate instantiation in C# where a single expression might correspond to multiple equality checks. E.g. x.compareTo(y) == 0 is a single expression that both acts as an equality check between the comparison and 0, and x and y.

[Copilot]

Pull Request Overview

Refactors the equality-check interface in the Guards library by replacing the old EqualityTest class with a versatile predicate and updating all its usages.

• Introduce predicate equalityTest(...) and remove the EqualityTest class in the shared QL signature.
• Add equalityTestSymmetric and replace eqtestHasOperands calls in the shared controlflow module.
• Remove Java-specific EqualityTest class and implement equalityTest predicate covering ==/!= and .equals(...) patterns.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
shared/controlflow/codeql/controlflow/Guards.qll	Remove EqualityTest class, add equalityTest predicate, update to use equalityTestSymmetric
java/ql/lib/semmle/code/java/controlflow/Guards.qll	Drop Java EqualityTest class, add equalityTest predicate to unify J::EqualityTest and equals calls

Comments suppressed due to low confidence (2)

shared/controlflow/codeql/controlflow/Guards.qll:353

• [nitpick] The parameter name eqval is ambiguous; consider renaming it to polarity to match the fourth parameter of equalityTest and improve clarity.

  private predicate equalityTestSymmetric(Expr eqtest, Expr e1, Expr e2, boolean eqval) {

java/ql/lib/semmle/code/java/controlflow/Guards.qll:299

• The predicate references class EqualityTest, but that class was removed earlier in this PR; this will cause a QL compilation error. You should refer directly to the built-in J::EqualityTest AST type (or reintroduce a local alias) before calling its getLeftOperand(), getRightOperand(), and polarity() methods.

    exists(EqualityTest eq | eq = eqtest |