Change meaning of unparameterized Tuple to Tuple[Any, ...] (== tuple) #2184

Currently, Type (without parameters) means a 0-length tuple, IOW Tuple[()] (which is the PEP 484 way to spell it). Analogy with List suggests it should be an unconstrained tuple, i.e. Tuple == tuple == Tuple[Any, ...]. The second half is already true. The List analogy is List == list == List[Any]. (The last part of that is spelled differently, but is a closer analogy to Tuple[Any, ...] than to Tuple[Any], since the latter is constrained to 1-length tuples.)