Support ignoring line ending format when comparing strings

[Bartleby2718]

Context

When you compare multi-line strings in NUnit test code, you often need to normalize line endings beforehand. A simple .Replace() will do, but:

1. it's annoying to put it everywhere.
2. the string replacement causes unnecessary memory allocations even when the string doesn't contain any newlines.

Proposal

A more user-friendly option would be handle this at the framework level, similar to the IgnoreCase modifier or the IgnoreWhiteSpace modifier which exist for some constraints.

Example

[Test]
public void TestIgnoringLineEndingFormat(string actual)
{
    const string expected = """
        multi-line
        raw
        string
        literal
        """;
    Assert.That(actual, Is.EqualTo(expected).IgnoreLineEndingFormat);
}