[mlir][ASM] Refactor how attribute/type aliases are specified.

Previously they were separated into "instance" and "kind" aliases, and also required that the dialect know ahead of time all of the instances that would have a corresponding alias. This approach was very clunky and not ergonomic to interact with. The new approach is to provide the dialect with an instance  of an attribute/type to provide an alias for, fully replacing the original split approach.

Differential Revision: https://reviews.llvm.org/D89354