Rtl-String: New tests

A set of tests of RtlUpcaseUnicodeString.
-Test#1: Upcases and forces to allocate a buffer.
-Test#2: Shows how RtlUpcaseUnicodeString accepts NULL as argument.
-Test#3: Upcases and forces to allocate the maximun buffer that an Unicode can use.
-Test#4: Shows how RtlUpcaseUnicodeString doesn't add a terminator to the Upcased string.

Hope they can be useful.
Thanks to ThFabba and Gigaherz to help while creating them