Various improvements to MakeFakeArguments.

Add an overload which takes a random number generator to enable generation of different random values in sequential calls to MakeFakeArguments. Add a mechanism for generating arrays of unique values (no duplicates) for the key inputs to key/value kSorts. Remove some sorcery in generating float arrays and replace with a uniform distribution. The underlying reason for using this strange distribution no longer exist.

PiperOrigin-RevId: 209083904