Rename helper functions in Yoneda

[dancewithheart]

Rename helper functions in Cubical.Categories.Yoneda:

• yo-yo-yo → yonedaToElement
• no-no-no → elementToYoneda

Partially addresses #1285.

[maxsnew]

What's the impetus for splitting it into two files?

[dancewithheart]

Splitting the
core Yoneda lemma (yoneda, yonedaᴾ, yoneda*, yonedaᴾ*) from the
embedding/application material (yo, YO, isFullYO, isFaithfulYO,
isFullyFaithfulYO) felt like a small cleanup in the spirit of #1267 (separating core
constructions from derived/application material).

[dancewithheart]

I restored the split into two files so this PR focuses only on the renaming cleanup and keeps the diff easier to review.

[maxsnew]

Thanks sorry about the delay. Typically we split files like this into Base which have just the core construction with minimal imports, and then Properties etc that may pull in more imports. So the correct style for this repo if we were to split the files would be to put the core in Cubical.Categories.Yoneda.Base, the other stuff in Cubical.Categories.Yoneda.Properties and then have a module Cubical.Categories.Yoneda that re-exports everything from Base and Properties. This helps to avoid circular dependencies. In this case, since the imports weren't any different between the two modules it doesn't really make much of a difference so I don't think we should bother.