[BasicAA] Enable separate storage hints by default (#76864)

As requested in
https://github.com/llvm/llvm-project/pull/76770#pullrequestreview-1801649466

A few months of experimentation in a large codebase did not reveal any
significant build speed regressions, and b07bf16a

 speeds up hint lookup
even further.

Co-authored-by: David Goldblatt <davidgoldblatt@meta.com>