C#: Add tests for Equals methods with nullable parameter types

[hvitved]

Adding tests to show that the two queries correctly handle Equals methods with nullable parameter types.

[Copilot]

Pull request overview

This PR adds test coverage for nullable parameter types in Equals methods to verify that the API abuse queries correctly handle nullable reference types. The tests validate that queries properly distinguish between nullable and non-nullable parameter types in both IEquatable<T>.Equals and object.Equals overrides.

Changes:

• Added test cases covering all combinations of nullable/non-nullable parameters for both Equals(T) and Equals(object) methods
• Implemented four test classes to validate different parameter type scenarios with nullable reference types enabled

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
csharp/ql/test/query-tests/API Abuse/IncorrectEqualsSignature/NullableTest.cs	Test cases for IncorrectEqualsSignature query with nullable parameter variations
csharp/ql/test/query-tests/API Abuse/ClassDoesNotImplementEquals/NullableTest.cs	Test cases for ClassDoesNotImplementEquals query with nullable parameter variations

[Copilot]

The null check param1 != null is ineffective because param1 is declared as non-nullable. With nullable reference types enabled, this parameter cannot be null under normal circumstances, making the null check unnecessary and potentially misleading.

Suggested change

	return param1 != null && field1 == param1.field1;
	return field1 == param1.field1;

[Copilot]

The null check param1 != null is ineffective because param1 is declared as non-nullable. With nullable reference types enabled, this parameter cannot be null under normal circumstances, making the null check unnecessary and potentially misleading.

Suggested change

	public bool Equals(TestClass4 param1)
	public bool Equals(TestClass4? param1)

[Copilot]

The null check param1 != null is ineffective because param1 is declared as non-nullable. With nullable reference types enabled, this parameter cannot be null under normal circumstances, making the null check unnecessary and potentially misleading.

Suggested change

	public bool Equals(TestClass2 param1)
	public bool Equals(TestClass2? param1)