Add option to ignore newline style when comparing strings for equivalency

[vbreuss]

Add the following option to the EquivalencyAssertionOptions<T> for strings

public EquivalencyAssertionOptions<T> IgnoringNewlineStyle()
{
    // This will replace "\r\n" with "\n" in actual and expected before comparison
    return this;
}

This fixes #2612 and fixes #2566

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