bringing back qiskit.transpiler.passes.LightCone (backport #15219)

[mergify]

Summary

Brings qiskit.transpiler.passes.optimization.light_cone.LightCone to qiskit.transpiler.passes.LightCone and updates the documentation links so it builds.

Details and comments

qiskit.transpiler.passes.LightCone was introduced in 2.0 and it is documented in that release as such. However, the 2.1 documentation does not include it, and since then it has not been possible to import it using from qiskit.transpiler.passes import LightCone. This PR restores that behavior.

I haven’t investigated why/how/when this API breakage occurred, and my memory is known to be ... weak. So, there’s a chance I’m missing some context, in which case this PR can be closed as wontfix.

---

This is an automatic backport of pull request #15219 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1f4811b has failed:

On branch mergify/bp/stable/2.2/pr-15219
Your branch is up to date with 'origin/stable/2.2'.

You are currently cherry-picking commit 1f4811b17.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   qiskit/circuit/__init__.py
	modified:   qiskit/transpiler/passes/__init__.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   qiskit/transpiler/passes/optimization/__init__.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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