GetFirstDerivedAttributeOrDefault implementation isn't consistent with doc comment

[Youssef1313]

Doc says:

/// Throws when multiple attributes are found (the attribute must allow multiple).

Implementation:

        Attribute[] cachedAttributes = GetCustomAttributesCached(attributeProvider, inherit);

        foreach (Attribute cachedAttribute in cachedAttributes)
        {
            if (AttributeComparer.IsDerived<TAttribute>(cachedAttribute))
            {
                return (TAttribute)cachedAttribute;
            }
        }

        return null;

My suggestion:

1. Remove the doc comment about throwing an exception and leave the method as-is
2. Introduce a new method that throws an exception and name it GetSingleDerivedAttributeOrDefault. Note that throwing exception may still be relevant even if AllowMultiple is not true (ONLY IF the attribute is not sealed). See UTA_MultipleExpectedExceptionsOnTestMethod is unused #4331 for details.
3. Revise all usages, and switch from GetFirstDerivedAttributeOrDefault to GetSingleDerivedAttributeOrDefault if needed.
4. My expectation is that after we do these three steps, we will end up having GetFirstDerivedAttributeOrDefault called with sealed attributes only. If this happened, we can switch all these to GetFirstNonDerivedAttributeOrDefault and delete GetFirstDerivedAttributeOrDefault