Accept nullable values in validation methods

[sephit]

Description

Resolves #17357

This PR modifies the parameters of the following methods as nullable values. This ensure that anyone can validate if a variable is null or not.

    [ContractAnnotation("value:null => halt")]
    public static T NotNull<T>(T value, T? value, [InvokerParameterName][NotNull] string parameterName)

    [ContractAnnotation("value:null => halt")]
    public static T NotNull<T>(T value, T? value, [InvokerParameterName][NotNull] string parameterName, string message) 

    [ContractAnnotation("value:null => halt")]
    public static string NotNull(string value, string? value, [InvokerParameterName][NotNull] string parameterName, int maxLength = int.MaxValue, int minLength = 0)

    [ContractAnnotation("value:null => halt")]
    public static ICollection<T> NotNullOrEmpty<T>(ICollection<T>? value, [InvokerParameterName][NotNull] string parameterName)

    public static T NotDefaultOrNull<T>(
        T? value,
        [InvokerParameterName][NotNull] string parameterName)
        where T : struct

Checklist

• I fully tested it as developer / designer and created unit / integration tests
• I documented it (or no need to document or I will create a separate documentation issue)

How to test it?

            string? value = null;
            Check.NotNullOrWhiteSpace(value, "value");

[CLAassistant]

All committers have signed the CLA.

[realLiangshiwei]

Thanks @sephit