[BasicAA] Generalize recursive phi alias analysis

For recursive phis, we skip the recursive operands and check that
the remaining operands are NoAlias with an unknown size. Currently,
this is limited to inbounds GEPs with positive offsets, to
guarantee that the recursion only ever increases the pointer.

Make this more general by only requiring that the underlying object
of the phi operand is the phi itself, i.e. it it based on itself in
some way. To compensate, we need to use a beforeOrAfterPointer()
location size, as we no longer have the guarantee that the pointer
is strictly increasing.

This allows us to handle some additional cases like negative geps,
geps with dynamic offsets or geps that aren't inbounds.

Differential Revision: https://reviews.llvm.org/D91914