Add public, py-less, substitute_node_with_dag to DAGCircuit

[eliarbel]

This commit adds the substitute_node_with_dag function to DAGCircuit as a public function, which does not require a py token to call.

This PR supports #14452

Details

The current implementation of substitute_node_with_dag supports qubits, clbits and variable mapping (through sustitute_node_with_subgraph). If no qubits or clbits mapping is provided by the caller (i.e. by sending None), a trivial mapping - i.e. mapping the qubits/clbits of the replacement DAG by order to the qargs/cargs of the node to be replaced - is generated. However, inferring trivial mapping for a node with variables is currently not implemented in this PR. So, in case of replacing a node with variables, the caller would need to define the mapping upfront and pass it to the function.

[coveralls]

Pull Request Test Coverage Report for Build 16446311540

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Details

• 116 of 144 (80.56%) changed or added relevant lines in 3 files are covered.
• 76 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.02%) to 87.759%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/circuit/src/dag_circuit.rs	114	142	80.28%

Files with Coverage Reduction	New Missed Lines	%
crates/circuit/src/dag_circuit.rs	1	85.39%
crates/qasm2/src/lex.rs	5	91.24%
crates/circuit/src/symbol_expr.rs	6	73.73%
crates/qasm2/src/parse.rs	6	97.56%
crates/transpiler/src/passes/gate_direction.rs	10	96.28%
crates/transpiler/src/target/mod.rs	48	84.99%

Totals
Change from base Build 16406114169:	-0.02%
Covered Lines:	81504
Relevant Lines:	92873

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💛 - Coveralls

[raynelfss]

FWIW, this solves #14512 . Linking it as issue to be closed by this PR.

[qiskit-bot]

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

• @Qiskit/terra-core

[eliarbel]

FWIW, this solves #14512 . Linking it as issue to be closed by this PR.

Thanks Ray, but this PR still misses one piece to be able to close #14512: if no qubits or clbits mapping are passed to substitute_node_with_dag, it defaults to using a trivial mapping. But this functionality is not yet implemented for variable mapping since inferring it is a bit more involved. It requires handling additional wires through additional_wires which uses a Python token. This PR is introduced for supporting the C API path (specifically for GateDirection), in which automatic inference of variable mapping is not required. I suggest we add the missing piece in a follow up PR. If agreed and this PR is merged as-is let's update #14512 to reflect the missing piece.