When loading a .ply file, warn about ignored properties

[emilk]

What

A .ply file can contain a lot of stuff, but we only support some of it.

This PR adds warning to the user about everything that was in the .ply file but couldn't be loaded (e.g. triangle faces, point normals, etc).

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

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