[flang] Add co_min and co_max to the list of intrinsics

Add the collective subroutines, co_min and co_max, to the list
of intrinsic subroutines. Add those two subroutines to the check
for coindexed objects for the first, third, and fourth dummy
arguments. Update the co_min and co_max semantics tests.

Reviewed By: klausler

Differential Revision: https://reviews.llvm.org/D133526