remove internal add_control

[1ucian0]

Summary

The internal function add_control seems to create confusion among users. Here some examples:

• sympy2symengine error in circuit transpilation #13161
• Invalid Parameters with CU gate in AerSimulator #12625
• Running a specific quantum circuit multiple times gets different state vectors #11458
• https://stackoverflow.com/a/59545389/8146172
• https://stackoverflow.com/q/71108162/8146172

I think it can be renamed to mitigate that effect.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[jakelishman]

I don't think we need to do this. It's not in the public interface, and I think changing its name like this risks suggesting that naming is what defines the public interface.

If we were going to do it, it'd probably be the module we renamed - the function itself is public within ourselves as a package (evidenced by how it's used in more than one file), and it's the module that's private to users.

[coveralls]

Pull Request Test Coverage Report for Build 13694788019

Warning: This coverage report may be inaccurate.

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Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 1305 unchanged lines in 39 files lost coverage.
• Overall coverage increased (+0.4%) to 88.507%

---

Files with Coverage Reduction	New Missed Lines	%
qiskit/circuit/_classical_resource_map.py	1	76.62%
qiskit/circuit/commutation_checker.py	1	94.12%
qiskit/circuit/controlflow/_builder_utils.py	1	96.97%
qiskit/circuit/parameterexpression.py	1	97.35%
qiskit/circuit/parameter.py	1	96.72%
qiskit/compiler/transpiler.py	1	98.78%
qiskit/transpiler/passes/layout/apply_layout.py	1	96.67%
qiskit/transpiler/passes/optimization/contract_idle_wires_in_control_flow.py	1	98.04%
qiskit/passmanager/passmanager.py	2	94.32%
crates/circuit/src/converters.rs	4	95.83%

Totals
Change from base Build 13687776352:	0.4%
Covered Lines:	71839
Relevant Lines:	81168

---

💛 - Coveralls

[1ucian0]

I renamed the module (and simplified one of the tests so it does not import the private module).

[alexanderivrii]

LGTM (and I have double-checked that add_control is not mentioned anywhere else in the Qiskit code). Just a few minor comments about the release notes.

[alexanderivrii]

Thanks @jakelishman for improving the release note.