Update Statevector and DensityMatrix evolve to work with operator qargs attr (Qiskit#3983)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: chriseclectic

qiskit/quantum_info/states/densitymatrix.py

@@ -216,6 +216,9 @@ def evolve(self, other, qargs=None):
             QiskitError: if the operator dimension does not match the
                          specified QuantumState subsystem dimensions.
         """
+        if qargs is None:
+            qargs = getattr(other, 'qargs', None)
+
         # Evolution by a circuit or instruction
         if isinstance(other, (QuantumCircuit, Instruction)):
             return self._evolve_instruction(other, qargs=qargs)

qiskit/quantum_info/states/statevector.py

@@ -197,6 +197,9 @@ def evolve(self, other, qargs=None):
             QiskitError: if the operator dimension does not match the
                          specified Statevector subsystem dimensions.
         """
+        if qargs is None:
+            qargs = getattr(other, 'qargs', None)
+
         # Evolution by a circuit or instruction
         if isinstance(other, (QuantumCircuit, Instruction)):
             return self._evolve_instruction(other, qargs=qargs)