Avoid intermediate DAGs in Optimize1qGatesDecomposition (#12176)

This commit removes the use of intermediate DAGCircuit objects and
calling substitute_node_with_dag() in the Optimize1qGatesDecomposition
pass. Since everything is 1q it's very easy to just directly insert the
nodes on the DAG prior to the run and then remove the old nodes. This
avoids a lot of extra operations and overhead to create a second dagcircuit
for each identified run and then substiting that dag in place of the
run.

qiskit/transpiler/passes/optimization/optimize_1q_decomposition.py

@@ -34,6 +34,7 @@
 )
 from qiskit.circuit import Qubit
 from qiskit.dagcircuit.dagcircuit import DAGCircuit
+from qiskit.dagcircuit.dagnode import DAGOpNode
 
 
 logger = logging.getLogger(__name__)
@@ -213,10 +214,15 @@ def run(self, dag):
             if best_circuit_sequence is not None and self._substitution_checks(
                 dag, run, best_circuit_sequence, basis, qubit
             ):
-                new_dag = self._gate_sequence_to_dag(best_circuit_sequence)
-                dag.substitute_node_with_dag(run[0], new_dag)
+                for gate_name, angles in best_circuit_sequence:
+                    op = NAME_MAP[gate_name](*angles)
+                    node = DAGOpNode(NAME_MAP[gate_name](*angles), run[0].qargs, dag=dag)
+                    node._node_id = dag._multi_graph.add_node(node)
+                    dag._increment_op(op)
+                    dag._multi_graph.insert_node_on_in_edges(node._node_id, run[0]._node_id)
+                dag.global_phase += best_circuit_sequence.global_phase
                 # Delete the other nodes in the run
-                for current_node in run[1:]:
+                for current_node in run:
                     dag.remove_op_node(current_node)
 
         return dag