Add Minitest/AssertEqualClass cop

[sambostock]

This cop enforces the test to use assert_instance_of instead of using assert_equal(Class, object.class).

# bad
assert_equal(Class, object.class)
assert_equal(Class, object.class, 'message')

# good
assert_instance_of(Class, object)
assert_instance_of(Class, object, 'message')

Arguably, this could be part of the Minitest/AssertInstanceOf cop, but that cop is metaprogramed, so would have to be reimplemented.

---

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• Added tests.
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[koic]

Arguably, this could be part of the Minitest/AssertInstanceOf cop, but that cop is metaprogramed, so would have to be reimplemented.

Yeah. It would be better to extend instead of metaprogramming for Minitest/AssertInstanceOf.

[koic]

@sambostock Can you reimplement Minitest/AssertInstanceOf instead of creating Minitest/AssertEqualClass? Minitest/AssertInstanceOf could be updated to an implementation that doesn't use MinitestCopRule and define_rule.

[koic]

@sambostock Will you continue to take this?

[koic]

I'm going to close this PR because this feature request will be resolved in #248. Thank you.