These were previously only accessible to admins, where we didn't filter
the ES results by their parent projects.

This adds the parent relation on project snippets, properly filters the
results for all the various cases, and aligns the ES snippet search
service and result classes to work more similarly to the other models.

#27703

- Use "results" instead of "blobs", "wiki blobs", "snippet blobs"
- Use "comments" instead of "notes"
- Use correct pluralization
- Don't add "1 - 10 of" if there's only one page