Improve the documentation of List and Data.List

This merge request aims to improve the documentation of the symbols exported from, and therefore displayed in the haddocks, of Data.List. A lot of the changes involve adding a collapsible header to existing examples, adding new examples where I felt they were needed, and in general making the documentation more accessible & easier to read.

Rendered Haddock (Expanded headers)

Rendered Haddock (Collapsed headers)

Even though I have looked through these changes numerous times, I'm sure I have missed mistakes somewhere in here, which is why I hope to get a few reviews in. The rendered haddocks above show artifacts due to this haddock bug and can be ignored.

Tracking: #17929 @Kleidukos @core-libraries