Add QuantumCircuit.find_bit to find index and Registers for a Bit. (Q…

…iskit/qiskit#6621)

* Add Register.index and Register._bit_indices.

* Add QuantumCircuit.find_bit to find index and Registers for a Bit.

* Add typing information and crossrefs to find_bit

* Revert accidental changes from base

* Add release note.

* Fix formatting in reno

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit_algorithms/linear_solvers/matrices/numpy_matrix.py

@@ -65,18 +65,19 @@ def __init__(
         self._evolution_time = None  # makes sure the eigenvalues are contained in [0,1)
         self._matrix = None
 
-        # store parameters
-        self.num_state_qubits = int(np.log2(matrix.shape[0]))
-        self.tolerance = tolerance
-        self.evolution_time = evolution_time
-        self.matrix = matrix
         super().__init__(
             num_state_qubits=int(np.log2(matrix.shape[0])),
             tolerance=tolerance,
             evolution_time=evolution_time,
             name=name,
         )
 
+        # store parameters
+        self.num_state_qubits = int(np.log2(matrix.shape[0]))
+        self.tolerance = tolerance
+        self.evolution_time = evolution_time
+        self.matrix = matrix
+
     @property
     def num_state_qubits(self) -> int:
         r"""The number of state qubits representing the state :math:`|x\rangle`.
@@ -181,7 +182,6 @@ def _reset_registers(self, num_state_qubits: int) -> None:
         """
         qr_state = QuantumRegister(num_state_qubits, "state")
         self.qregs = [qr_state]
-        self._qubits = qr_state[:]
 
     def _build(self) -> None:
         """Build the circuit"""