Documentation: Improve Foldable1 documentation
- Explain foldrMap1, foldlMap1, foldlMap1', and foldrMap1' in greater detail, the text is mostly adapted from documentation of Foldable.
- Describe foldr1, foldl1, foldl1' and foldr1' in terms of the above functions instead of redoing the full explanation.
- Small updates to documentation of fold1, foldMap1 and toNonEmpty, again adapting from Foldable.
- Update the foldMap1 example to lists instead of Sum since this is recommended for lazy right-associative folds.
Fixes #22847 (closed)