[mlir][llvm] Use interfaces in the translation to LLVMIR.

The revision consistently uses the AliasAnalysisOp and AccessGroupOp
interfaces in the translation from MLIR to LLVMIR. It thus drops the
last string based lookups of alias scope and access group attributes.

Depends on D144851

Reviewed By: Dinistro

Differential Revision: https://reviews.llvm.org/D145037