[Attributor] Derive better alignment for accessed pointers

Use DL & ABI information for better alignment deduction, e.g., if a type
is accessed and the ABI specifies an alignment requirement for such an
access we can use it. This is based on a patch by @lebedev.ri and
inspired by getBaseAlign in Loads.cpp.

Depends on D76673.

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D76674