[AQT] Vendor Transformer adoption

[MichaelBroughton]

Summarize the task
With broader changes to devices (#4744) and optimizers/trasnformers (#4722), vendors might need to update device decomposition to use the newest transformer APIs. At first glance it looks like:

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cirq-aqt uses cirq native ion devices which have had their decompose_operation method deprecated in favor of cirq.ConvertToIonGates():

Cirq/cirq-aqt/cirq_aqt/aqt_device.py

Line 221 in 45624ff

def get_aqt_device(num_qubits: int) -> Tuple[cirq.IonDevice, List[cirq.LineQubit]]:

which is defined here:

Cirq/cirq-core/cirq/ion/convert_to_ion_gates.py

Line 21 in 45624ff

class ConvertToIonGates:

Should we move this to cirq-aqt and convert to a transformer to try and consolidate some code here. WDYT @tanujkhattar and @ma5x @pschindler @alfrisch

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