Update nanoflann to version 1.5.0

[roehling]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Maintenance of third-party dependencies, in this case nanoflann

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

This PR updates Open3D to build with the latest nanoflann version 1.5.0. Note that Jose did some refactoring, so this PR makes Open3D incompatible with older nanoflann releases.

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This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[roehling]

It looks like the unit test is failing for the new Nanoflann. I'll convert this into a Draft pending further investigation.

[roehling]

I found and fixed the issue; the PR is ready for review now.

[ssheorey]

Note that Jose did some refactoring, so this PR makes Open3D incompatible with older nanoflann releases.

In that case, can you add a check in find_dependencies.cmake that gives a fatal error if USE_SYSTEM_NANOFLANN but the version is less than 1.5?

[roehling]

Good point.

[ssheorey]

Thanks as always @roehling !