[AArch64] Add and expand the testing of fmin/fmax reduction. NFC

[AArch64] Add and expand the testing of fmin/fmax reduction. NFC

For both CodeGen and CostModelling, this adds extran testing for the new
lvm.vector.reduce.fmaximum and lvm.vector.reduce.fminimum intrinsics, as well
as making sure there is test coverage for all the various cases.