Add optimization for TwoLocal synthesis when entanglement='full'

[ShellyGarion]

Summary

close #8294
Update the NLocal class.

Details and comments

When choosing a TwoLocal or RealAmplitude or EfficientSU2 gate with entanglement=full on n-qubits (for VQE ansatz),
for a circuit with a CX sub-circuit, improve the number of CX gates from n*(n-1)/2 CX gates to only n-1 CX gates with a linear connectivity

[qiskit-bot]

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the the following people are requested to review this:

• @Cryoris
• @Qiskit/terra-core
• @ajavadia

[coveralls]

Pull Request Test Coverage Report for Build 2782954860

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.005%) to 83.99%

---

Files with Coverage Reduction	New Missed Lines	%
qiskit/extensions/quantum_initializer/squ.py	2	80.9%

Totals
Change from base Build 2781722893:	0.005%
Covered Lines:	55903
Relevant Lines:	66559

---

💛 - Coveralls

[Cryoris]

Looks pretty good to me, I think it would be nice to explain this optimization somewhere -- either in the NLocal docstring or in an extended comment inside the code.

[ShellyGarion]

I agree that we should add a docstring explaining this optimization, and will do it after finalizing the API.

[Cryoris]

I think this is almost good to go! Two more things: Could you add a releasenote, and could you check the reverse_linear entanglement works if it is used in the ZZFeatureMap?

[ShellyGarion]

@Cryoris - thanks for the quick and helpful review. I think this PR is ready to go now.

[Cryoris]

LGTM thanks for this feature!