[flang][OpenMP] Use maxnum/minnum for lowering of max/min reduction operators (#89258)

This patch changes the lowering of max and min to be lowered to
arith::MaxNumFop and arith::MinNumFOp instead of using arith::MaximumFOp
and arith::MinimumFOp. The arith::MaximumFOp and arith::MinimumFOp map
to the corresponding intrinsics llvm.maximum.* and llvm.minimum.*
intrinsics which conform to the semantics specified in the draft of IEEE
754-2019, which is not supported by all hardware. Instead using
arith::MaximumFOp and arith::MinimumFOp will allow code generation for
more targets and match the code generated by clang OpenMP.

fixes #87955