Migrate StrategyExecutor to new transformer infrastructure

[ammareltigani]

Migrated the StrategyExecutor class to strategy_executor() function that uses transformer_primitives. Depreciated StrategyExecutor.

[tanujkhattar]

Looks like a good start, I've left some comments. Please let me know if you have questions!

[tanujkhattar]

Left another round of comments.

[ammareltigani]

I changed the argument and return type for the circuit that is being modified in the __call__ function of StrategyExecutorTransformer to circuits.Circuit (instead of accepting circuits.AbstractCircuit and returning circuits.Circuit for the reasons we discussed) and also reflected this change in the __call__ function of ExecutionStrategy.

This is because the method expose_acquaintance_gates accepts a circuit of type circuits.Circuit (not circuits.AbstractCircuit), so the type checker was complaining when I made the argument of type circuits.AbstractCircuit.

I thought of changing the type of the circuit in the method signature of __call__ in ExposeAcquaintanceGates but it seems like this could be a breaking change since with are accessing _moments in a method of that class, which is a property of circuits.Circuit but not of circuits.AbstractCircuit

[pavoljuhas]

...
FAILED dev_tools/docker_test.py::test_docker_pre - AssertionError: assert 1 == 0
FAILED dev_tools/docker_test.py::test_docker_stable - AssertionError: assert ...
2 failed, 16372 passed, 93 skipped, 132 xfailed, 504 warnings in 277.64s (0:04:37)

I also get those 2 failures when running tests locally, I suspect they need docker installation to pass.
You can ignore those two unless your PR makes some changes to the Dockerfile.

[tanujkhattar]

Looking pretty good; a final round of comments!

[tanujkhattar]

Looks great, thanks for all the iterations!