[flang] Allow PDTs with LEN parameters in REDUCE()

The type compatibility checks for the ARRAY= argument and the dummy
arguments and result of the OPERATION= argument to the REDUCE intrinsic
function need to allow for parameterized data types with LEN parameters.
(Their values are required to be identical but this is not a numbered
constraint requiring a compilation time check).

Differential Revision: https://reviews.llvm.org/D125124