Method to capture additional keyword arguments to transformers while preserving mypy type.

Returns a cirq.TRANSFORMER which, when called with a circuit and transformer context, is equivalent to calling transformer(circuit, context=context, **kwargs). It is often useful to capture keyword arguments of a transformer before passing them as an argument to an API that expects cirq.TRANSFORMER. For example:

def run_transformers(transformers: 'List[cirq.TRANSFORMER]'):
    circuit = cirq.Circuit(cirq.X(cirq.q(0)))
    context = cirq.TransformerContext()
    for transformer in transformers:
        transformer(circuit, context=context)

transformers: 'List[cirq.TRANSFORMER]' = []
        cirq.expand_composite, no_decomp=lambda op: cirq.num_qubits(op) <= 2
transformers.append(cirq.create_transformer_with_kwargs(cirq.merge_k_qubit_unitaries, k=2))

transformer A cirq.TRANSFORMER for which additional kwargs should be captured.
**kwargs The keyword arguments which should be captured and passed to transformer.

A cirq.TRANSFORMER method transformer_with_kwargs, s.t. executing transformer_with_kwargs(circuit, context=context) is equivalent to executing transformer(circuit, context=context, **kwargs).

SyntaxError if **kwargs contain a 'context'.