Migration of optimizers in vendor packages to new transformers infrastructure.

[tanujkhattar]

Summarize the task After https://github.com/quantumlib/Cirq/issues/4722, all optimizers in cirq-core have been migrated to the new transformer API https://github.com/quantumlib/Cirq/issues/4483, re-implemented using new moment-preserving transformer primitives and support no-compile tags.

This issue is to track the migration of all optimizers in cirq's vendor packages to the new transformer infrastructure.

Acceptance criteria - when is the task considered done? When the following optimizers have been migrated to new transformer infrastructure.

cirq-google

• [x] ConvertToXmonGates
• [x] ConvertToSqrtIswapGates
• [x] ConvertToSycamoreGates
• [x] optimized_for_xmon
• [x] optimized_for_sycamore
• [x] _PhasedFSimConverter

cirq-ionq

• [x] ionq_devices/decompose_to_device

cirq-pasqal

• [x] PasqalConverter

cirq-core/ion

• [x] ConvertToIonGates

cirq-core/neutral-atoms

• [x] ConvertToNeutralAtomGates

cirq-corq/contrib

• [x] ConvertToSingleQubitCliffordGates
• [x] ConvertToPauliStringPhasors
• [x] StrategyExecutor
• [x] SwapPermutationReplacer
• [x] MergeNQubitGates

Note that most of the Convert* type optimizers can be replaced with the newly added cirq.optimize_for_target_gateset transformer. To do the migration, user would just need to create a new target gateset that can be used as an argument to the above transformer. The new gateset can be simply created by deriving from cirq.TwoQubitCompilationTargetGateset. See https://github.com/quantumlib/Cirq/pull/5007 for a sample migration PR.

Part of roadmap: https://github.com/quantumlib/Cirq/issues/3238

[dstrain115]

I updated Pasqal and neutral atoms, which are now converted.

@tanujkhattar Can you update this list? optimize_for_xmon is now replaced by optimize_for_target_gateset, right? Are any of the other optimizers completed?

[tanujkhattar]

This is now complete.