Patched and tested the `AAInvariantLoadPointer` attributor from #141800,
which identifies pointers whose loads are eligible to be marked as
`!invariant.load`.

The bug in the attributor was due to `AAMemoryBehavior` always
identifying pointers obtained from `alloca`s as having no writes. I'm
not entirely sure why `AAMemoryBehavior` behaves this way, but it seems
to be beceause it identifies the scope of an `alloca` to be limited to
only that instruction (and, certainly, no memory writes occur within the
`alloca` instructin). This patch just adds a check to disallow all loads
from `alloca` pointers from being marked `!invariant.load` (since any
well-defined program will have to write to stack pointers at some
point).

Reverts llvm/llvm-project#141800

The implementation critically misunderstands the `AAMemoryBehavior`
attributor, which it relies on heavily.

@shiltian, since I do not have commit permissions.

The attributor conservatively marks pointers whose loads are eligible to
be marked as `!invariant.load`.
It does so by identifying:
1. Pointers marked `noalias` and `readonly`
2. Pointers whose underlying objects are all eligible for invariant
loads.

The attributor then manifests this attribute at non-atomic non-volatile
load instructions.

If the underlying object already has a non-flat address space, we simply
use
that before calling `getAssumedAddrSpace`.

Partially fixes SWDEV-536263.

This reverts commit 37ea3b32cdcb6c0dcecbcc4bf844f5190c7378dd.

This reverts commit 4efc13f8ff1eaf4f9fb1fcea8d4552b3eca052ca.

This reverts commit 3c6211c183885afb5d89259a53c4f4f46a6bf399.

This reverts commit 9bf6b2a8cb0467b62173659306e43a0346f063a2.