Patch support for Eigen5

[Timple]

This is a (rather not-so-nice looking) fix to support Eigen5.

The issue is not yours, but this patch will add support until strasdat/Sophus#558 is fixed upstream.

Proposed changes

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If it fixes a bug or resolves a feature request, be sure to link to that issue.

Type of change

• 🐛 Bugfix (change which fixes an issue)
• 🚀 Feature (change which adds functionality)
• 📚 Documentation (change which fixes or extends documentation)

💥 Breaking change! Explain why a non-backwards compatible change is necessary or remove this line entirely if not applicable.

Checklist

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• Lint and unit tests (if any) pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• All commits have been signed for DCO

Additional comments

Anything worth mentioning to the reviewers.

[glpuga]

Thanks, we'll take a look!

[Timple]

Thank you! It's finished and validated now.

Didn't validate against packages depending on this one, so that got me two regressions which I solved now.