update: collection-aggregate.md (#2547)
update: collection-aggregate.md (#2547)

* Update collection-aggregate.md

Update collection-aggregate.md to fix the incorrectly documented relationship between "by" max/min functions (`maxByOrNull`) and "of" max/min functions (`maxOfOrNull`). The current documentation says that `maxByOrNull` and `maxOf` are the same except for how they handle empty corrections. I believe this is incorrect because `maxOf` also returns a selector return value, not a collection element. In addition, the current documentation does not mention some functions, such as `maxOfOrNull` and `maxOfWithOrNull`.

This is my first time contributing to the docs; please let me know if I made a mistake or am misunderstanding something.

* Update collection-aggregate.md

* Update collection-aggregate.md

Minor phrasing improvement

* Update collection-aggregate.md

Co-authored-by: Pavel Semyonov <9fef4c3b275d1b1cf2d37bb4fde2472935675f02@users.noreply.github.com>
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