[Attributor] Allow not to default initialize AAs for live internal functions

[Attributor] Allow not to default initialize AAs for live internal functions

Outside users of the Attributor, e.g., OpenMP-opt, want to seed AAs
themselves. We should not seed all default AAs one an internal function
becomes live. That said, there should be a callback such that they can
do lazy seeding as well.

Differential Revision: https://reviews.llvm.org/D121489