Add densmap component

[jakubmajercik]

Changelog

densMAP dimensionality reduction component implemented. Neighbor computing updated to output KNN results as input to densMAP. Test resources need to be updated to include these extra fields in the mudata/anndata objects.

Issue ticket number and link

Closes #739

Checklist before requesting a review

• [x] I have performed a self-review of my code

• [ ] Conforms to the Contributor's guide

• Check the correct box. Does this PR contain:

  • [ ] Breaking changes
  • [x] New functionality
  • [ ] Major changes
  • [ ] Minor changes
  • [ ] Documentation
  • [ ] Bug fixes

• [x] Proposed changes are described in the CHANGELOG.md

• [ ] CI tests succeed! - failing due to modified neighbor computing component.