Add new get_control_flow_name_mapping function

[ElePT]

Summary

Addresses #13468 by exposing the mapping done in generate_preset_pass_manager as a public function for convenience.

Details and comments

[qiskit-bot]

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

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 11976548054

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Details

• 7 of 7 (100.0%) changed or added relevant lines in 3 files are covered.
• 29 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.03%) to 88.919%

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Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/two_qubit_decompose.rs	1	92.13%
crates/qasm2/src/lex.rs	4	91.48%
crates/qasm2/src/parse.rs	24	96.23%

Totals
Change from base Build 11944955850:	-0.03%
Covered Lines:	79391
Relevant Lines:	89285

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💛 - Coveralls

[wshanks]

The way this is implemented matches how it has been used so I think it is good. One point that we should note at least is that the standard gate version of this function returns a mapping to gate instances while the control flow function here returns a mapping to classes. The gates version gets away with this by using Parameters to fill in the gate parameters, but I don't think there are reasonable equivalents for the conditions and bodies of the conditionals (could use size 1 registers and empty circuits but it seems weird).

By the way, you can also replace this case:

qiskit/qiskit/providers/backend_compat.py

Lines 94 to 99 in 5f3f594

	qiskit_control_flow_mapping = {
	"if_else": IfElseOp,
	"while_loop": WhileLoopOp,
	"for_loop": ForLoopOp,
	"switch_case": SwitchCaseOp,
	}

[ElePT]

Thanks @wshanks! I applied your suggestion in 5434583. you're right, the function doesn't match the gate version exactly, but I also didn't find any reasonable way to instantiate the gates, and tried to avoid making the parallelism in the docs for that reason. There is a risk that users might still associate them but well... we could always highlight the difference in documentation if necessary.