Reformat pyext to avoid merge conflicts

[jakelishman]

Summary

Since we're still in a phase of adding many new extension modules to pyext, the current structure of the file is causing problems with most commits hitting merge conflicts in the use block. This changes the style of the file so that each new module takes only a single line, which is more friendly to avoiding merge conflicts, and fixing them when they arise.

Details and comments

I don't feel super strongly about this, just it's been a slight annoyance I've seen a few people have, and I just did too.

[qiskit-bot]

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

• @Qiskit/terra-core
• @kevinhartman
• @mtreinish

[ElePT]

As a merge conflict victim, I'd be in favor of the change :)

[coveralls]

Pull Request Test Coverage Report for Build 10945790303

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

• 34 of 34 (100.0%) changed or added relevant lines in 1 file are covered.
• 26 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.03%) to 88.764%

---

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/two_qubit_decompose.rs	1	91.45%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	2	88.26%
crates/qasm2/src/lex.rs	4	91.98%
qiskit/synthesis/two_qubit/xx_decompose/decomposer.py	7	90.91%
crates/qasm2/src/parse.rs	12	96.69%

Totals
Change from base Build 10945433225:	-0.03%
Covered Lines:	73461
Relevant Lines:	82760

---

💛 - Coveralls

[jakelishman]

Huh, that lint failure is a true lint failure - that function doesn't exist, but I'm curious why lint didn't fail on #12959, which is what actually removed it. I'll fix it in a separate PR.

[jakelishman]

Ok, rebased and now this should pass lint.