Allow NUnit2005 to recognize Is.Empty

[RenderMichael]

We have the following code:

Assert.AreEqual(string.Empty, element.GetDomProperty("value"));
Assert.AreEqual("", element.GetDomProperty("value"));

The NUnit2005 fixer transforms these into

Assert.That(element.GetDomProperty("value"), Is.EqualTo(string.Empty));
Assert.That(element.GetDomProperty("value"), Is.EqualTo(""));

Both of these could become Is.Empty instead

[manfred-brands]

@RenderMichael Yes, it could, but that wouldn't be a direct conversion of the AreEqual but of Assert.IsEmpty
But as it is better code, I agree.

There are a few more use cases:

Assert.AreEquals(Guid.Empty, value);
Assert.AreEqual(Enumerable.Empty<char>(), value);
Assert.AreEqual(Array.Empty<char>(), value);
Assert.AreNotEqual(String.Empty, value);
Assert.AreNotEqual(ImmutableArray<int>.Empty, value);