[mlir] NFC: Move the state for managing aliases out of ModuleState and into a new class AliasState.

Summary: This reduces the complexity of ModuleState and simplifies the code. A future revision will mold ModuleState into something that can be used by users for caching of printer state, as well as for implementing printAsOperand style methods.

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D72292