Reaction summary view and sorting reactions by count and then timestamp (#942)

* Sort reactions by count and then timestamp

- Sort reactions within an aggregation by timestamp descending. This puts the most recent at the top, useful in cases like the reaction summary view or getting the most recent reaction.
- Sort aggregated reactions by count and then timestamp ascending, using the most recent reaction in the aggregation. This appends new aggregations on the end of the reaction layout.

* Add reaction summary view

* fix warnings

* Fix test unit tests and add sorting tests

- Fix broken build in test code
- Add a test for reaction sorting

* Remove default closure, move logic to presenter and add tests

* Update screenshots

* Fix imports

* Revert Screenshots I didn't update

* Fix imports remove screetshots

* Update screenshots

* Update screenshots

* Address comments.

* Update screenshots

* Remove unnecessary snapshotFlow

* Fix code quality checks

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Co-authored-by: ElementBot <benoitm+elementbot@element.io>

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