[mlir][spirv] Unify aliases of different bitwidth scalar types

This commit extends the UnifyAliasedResourcePass to handle scalar
types of different bitwidths. It requires to get the smaller bitwidth
resource as the canonical resource so that we can avoid subcomponent
load/store. Instead we load/store multiple smaller bitwidth ones.

Reviewed By: hanchung

Differential Revision: https://reviews.llvm.org/D127266