#553 normalize-unicode() second arg must be uppercase

[Michael Kay]

Saxon's implementation of normalize-unicode() requires
the second argument (the name of the normalization
form) to be in upper case, for example "NFC". The spec
allows mixed upper and lower case.

Test case: fn-normalize-unicode2args-2

(Note also, Saxon 8.7.3 first checks to see if the
first argument contains any non-ASCII characters. If it
does, then the second argument is examined. This means
that errors in the second argument are not necessarily
detected. This is conformant, but will be changed for
usability reasons.)