Tests for read/unread status (#11301)

* Add some fantasy tests

* Turn commented code into pretend-real code

* First pass at a list of all the cases we should test

* List test cases related to redactions

* Add testcases about paging up

* Add a case about notification counts

* More test cases related to replies, notifications, room list

* Iterate tests

* Wire up additional tests

* Wire up more tests

* Tidy

* Wire up more tests

* Wire up more tests

* Wire up more tests

* Wire up more tests

* Mute browser

* Silence electron warnings

* Iterate

* revert

* Wire up more tests

* Try to stabilise tests

* Try to stabilise tests

* Validate that the notification dot is missing as well as the count

* Skip a test that is failing for unknown reasons

* Use markAsRead in 'marking as read' test and add related test

* Fix incorrect comment

* Extract tests to their own suite

* Attempt to fix test

* Wire up more tests

* Wire up more tests

* Wire up more tests

* Wire up more tests

* Iterate

* Add comments

* Iterate

* Fix comments

* Update cypress/e2e/read-receipts/high-level.spec.ts

Co-authored-by: Richard van der Hoff <[email protected]>

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Co-authored-by: Michael Telatynski <[email protected]>
Co-authored-by: Richard van der Hoff <[email protected]>