Fix pip-compile package ordering

[adamsol]

Closes #1414.

Changelog-friendly one-liner: Fix pip-compile package ordering to match that of pip freeze.

Contributor checklist

• Provided the tests for the changes.
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[ssbarnea]

I am a little bit against this change because it would break sorting using cli sort or editor sorting, which does the sorting line by line. In fact I would support pip freeze update to address this and making it compliant. I am wondering what others think.

[adamsol]

I think that the current pip freeze's behaviour makes more sense, and generic sorting utilities aren't the right tool for this job anyway. I doubt anyone would expect or want the = character to take part in the sorting. And even ignoring the lexicographic order of package names, those utilities won't handle urls or comments in the file properly. Also note that the order of packages after running a line-by-line sort on requirements.in (without version specifiers) can be different than for the resulting requirements.txt.

[atugushev]

LGTM 👍