[Attributor][NFCI] Avoid creating unnecessary AAs

If the IR has a boolean attribute, or the function is not IPO amendable,
we can avoid creating AAs that would just be forced into a trivial
fixpoint anyway. Since we check boolean IR attributes via
`AA::hasAssumedIRAttr`, we don't need AAs even if they would be fixed
optimistic right away. The only change is in the dependency graph
ordering as we move AAs around to simplify the code flow. There is no
reason for the order we seed AAs, so this order is just as fine.