[mlir] Move affine's FoldMemRefAliasOps into its own pass (#172548)
I'm planning to introduce an interface that'll allow FoldMemRefAliasOps
to not know about dialects like NVVM or GPU. To do this, however, I need
to get the `affine` ops (which need special handling in order to handle
their implicit affine maps) into a separate pass, analogously to how
`amdgpu` ops have these patterns under their dialect and ton under
`memref`.
This commit also changes the expand/collapse_shape index resolvers to
return `void`, since they never actually failed and to make it clearer
that they modify IR.
(Note: An LLM did the initial refactoring and test movement, I've
reviewed the results and edited them some.)
llvm-project
003b28d0 - [mlir] Move affine's FoldMemRefAliasOps into its own pass (#172548)
