[Attributor] Add AAAddressSpace to deduce address spaces

This patch adds initial support for the `AAAddressSpace` abstract
attributor interface to deduce and query address space information for a
pointer. We simply query the underlying objects that a pointer can point
to and find a common address space if they exist. This is the minimal
support for the interface, we currently manifest changes on loads and
stores. Additionally we should use the target transform information to
deduce if an address space transformation is a no-op for the target
machine when calculating compatibility.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D120586