Use a more efficient and actually correct circuit for ECR target

The previous definition of a swap gate using ECR rz and sx was incorrect
and also not as efficient as possible. This was missed because the tests
were accidently broken since Qiskit#10314 which was fixed in the previous
commit. This commit updates the definition to use one that is actually
correct and also more efficient with fewer 1 qubit gates.

Co-authored-by: Alexander Ivrii <alexi@il.ibm.com>

qiskit/circuit/library/standard_gates/equivalence_library.py

@@ -869,29 +869,16 @@ def _cnot_rxx_decompose(plus_ry: bool = True, plus_rxx: bool = True):
 # «     └──────────┘                 └──────┘└─────────┘ └────┘└──────────┘
 #
 q = QuantumRegister(2, "q")
-def_swap_ecr = QuantumCircuit(q, global_phase=pi / 2)
-def_swap_ecr.rz(pi / 2, 0)
-def_swap_ecr.sx(0)
-def_swap_ecr.rz(pi / 2, 1)
-def_swap_ecr.sx(1)
-def_swap_ecr.rz(-pi, 1)
-def_swap_ecr.ecr(0, 1)
-def_swap_ecr.rz(pi / 2, 1)
-def_swap_ecr.sx(1)
-def_swap_ecr.rz(pi / 2, 0)
-def_swap_ecr.sx(0)
-def_swap_ecr.rz(-pi, 0)
-def_swap_ecr.ecr(0, 1)
-def_swap_ecr.rz(pi / 2, 0)
-def_swap_ecr.sx(0)
+def_swap_ecr = QuantumCircuit(q)
 def_swap_ecr.rz(-pi / 2, 0)
+def_swap_ecr.sx(1)
 def_swap_ecr.ecr(0, 1)
-def_swap_ecr.rz(-pi / 2, 0)
+def_swap_ecr.rz(-pi / 2, 1)
 def_swap_ecr.sx(0)
+def_swap_ecr.ecr(1, 0)
 def_swap_ecr.rz(-pi / 2, 0)
-def_swap_ecr.rz(pi / 2, 1)
 def_swap_ecr.sx(1)
-def_swap_ecr.rz(-pi / 2, 1)
+def_swap_ecr.ecr(0, 1)
 _sel.add_equivalence(SwapGate(), def_swap_ecr)
 
 # SwapGate