Sets the value of global constant cirq.__cirq_debug__ within the context.

If __cirq_debug__ is set to False, all validations in Cirq are disabled to optimize performance. Users should use the cirq.with_debug context manager instead of manually mutating the value of __cirq_debug__ flag. On exit, the context manager resets the value of __cirq_debug__ flag to what it was before entering the context manager.