Complete UChar implementation

[NightOwl888]

In Java, the UCharacter class has all of the same APIs as the java.lang.Character class. Therefore, in .NET, we need UChar to cover the same APIs (static methods) as System.Char.

We need more clarity on specifically how to design the culture-sensitivity part of this, since in Java these methods were designed to use the equivalent of CultureInfo.InvariantCulture and therefore are not aware of the ambient culture.

We also need tests to validate expected behaviors with the new methods.