[MLIR] Place async.drop_ref operations when identical code folding is applied to basic blocks.

[erick-xanadu]

The requirement here identical code folding (also known as mergeIdenticalBlocks) can be run before the add-exception-handling-pass. See ticket #995 . Something that would also be good is improve the pass pipeline interface for conditional passes. Something like:

        "convert-catalyst-to-llvm",
        "convert-quantum-to-llvm",
        "convert-async-to-llvm" if config.async else None,  # or `else ""`
        "add-exception-handling",
        "emit-catalyst-py-interface",

Would be nice.