[llvm][Attributor] Strip AddressSpaceCast from 'constructPointer' (#74742)

* Remove pointer AddressSpaceCast in function `constructPointer`
* Remove 1st parameter (`ResTy`) of function `constructPointer`

1st input argument to function `constructPointer` in all 4 call-sites is
`ptr addrspace(0)`. Function `constructPointer` performs a pointer
AddressSpaceCast to `ResTy`, making the returned pointer have type `ptr
addrspace(0)` in all 4 call-sites.

Unless there's a clear reason to discard the addrspace info of input
parameter `Ptr`, I think we should keep and forward that info to the
returned pointer of `constructPointer`.

Opaque ptr cleanup effort.