RCS1224: Make method an extension method

Summary

Public/internal method in public/internal static class whose name ends with "Extensions" should be an extension method.

public static class FooExtensions
{
    public static string Bar(Foo foo) // RCS1224
    {
    }
}

public static class FooExtensions
{
    public static string Bar(this Foo foo)
    {
    }
}