Extend SubstitutePi4Rotations to 2q gates

[ShellyGarion]

Summary

close #15381

The SubstitutePi4Rotations transpiler pass now handles two types of gates:

• rotation gates: 1-qubit: RX, RY, RZ, P, U1, and 2-qubit: RZZ, RZX, RXX, RYY,
• controlled-rotation gates: CP, CRZ, CRY, CRX, CU1.

For the rotation gates, when their angle is a multiple of pi/4, they can be converted into {Clifford, T, Tdg} with a single T/Tdg gate. For even multiples, they can be written using only Clifford gates.

For the controlled-rotation gates, when their angle is a multiple of pi/2, they can be converted into {Clifford, T, Tdg} with 3 T/Tdg gates for CP and 2 T/Tdg gates otherwise. For even multiples, they can be written using only Clifford gates.

This PR also aims to reduce the total number of Clifford gates in the decompositions.

Details and comments

Note that since we should also replace 2-qubit gates (and not only 1-qubit gates), we need to construct a new DAG instead of replacing the nodes inplace.

This can make this pass slower compared to the existing code, by a factor 2x.
E.g. for a 20-qubit circuit with 10000 gates, containing a percenentage p of 1-qubit rotation gates, the total time is:

percentage	main branch	this PR	ratio
0.1	0.03	0.07	2.3
0.25	0.05	0.09	1.8
0.5	0.06	0.11	1.8
0.75	0.07	0.15	2.1
0.9	0.08	0.15	1.8

[coveralls]

Pull Request Test Coverage Report for Build 20696382817

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 69 of 75 (92.0%) changed or added relevant lines in 1 file are covered.
• 18 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.004%) to 88.314%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/transpiler/src/passes/substitute_pi4_rotations.rs	69	75	92.0%

Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/optimization/substitute_pi4_rotations.py	1	91.67%
crates/qasm2/src/lex.rs	5	92.29%
crates/qasm2/src/parse.rs	12	96.62%

Totals
Change from base Build 20366546417:	0.004%
Covered Lines:	96757
Relevant Lines:	109560

---

💛 - Coveralls

[qiskit-bot]

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

• @Qiskit/terra-core