Fix converting VectorStateFn to a CircuitStateFn

[Cryoris]

Summary

Fix converting a VectorStateFn to a CircuitStateFn, which previously resulted in a StateFn that couldn't be adjoint.

Details and comments

Previously it was not possible to adjoint a CircuitStateFn that has been
constructed from a VectorStateFn, because the statevector has been
converted to a circuit with the Initialize instruction, which
is not unitary. This problem is now fixed by instead using the StatePreparation
instruction, which can be used since the state is assumed to start out in the all 0 state.

For example we can now do:

from qiskit import QuantumCircuit
from qiskit.opflow import StateFn

left = StateFn([0, 1])
left_circuit = left.to_circuit_op().primitive

right_circuit = QuantumCircuit(1)
right_circuit.x(0)

overlap = left_circuit.inverse().compose(right_circuit)  # this line raised an error before!

This also enables using initial states in #8304.

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[coveralls]

Pull Request Test Coverage Report for Build 2747142077

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 83.994%

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Totals
Change from base Build 2745932216:	0.007%
Covered Lines:	55897
Relevant Lines:	66549

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💛 - Coveralls