Sliding sync: add missing filters from latest MSC

* Retry to-device messages

This adds a queueToDevice API alongside sendToDevice which is a
much higher-level API that adds the messages to a queue, stored in
persistent storage, and retries them periodically. Also converts
sending of megolm keys to use the new API.

Other uses of sendToDevice are nopt converted in this PR, but could
be later.

Requires matrix-org/matrix-mock-request#17

* Bump matrix-mock-request

* Add more waits to make indexeddb tests pass

* Switch some test expectations to queueToDevice

* Stop straight away if the client has been stopped

Hopefully will fix tests being flakey and logging after tests have
finished.

* Add return types & fix constant usage

* Fix return type

Co-authored-by: Germain <germains@element.io>

* Fix return type

Co-authored-by: Germain <germains@element.io>

* Fix return type

Co-authored-by: Germain <germains@element.io>

* Stop the client in all test cases

Co-authored-by: Germain <germains@element.io>

)

* Add support for sending user-defined encrypted to-device messages

This is a port of the same change from the robertlong/group-call branch.

* Fix tests

* Expose the method in MatrixClient

* Fix a code smell

* Fix types

* Test the MatrixClient method

* Fix some types in Crypto test suite

* Test the Crypto method

* Fix tests

* Upgrade matrix-mock-request

* Move useRealTimers to afterEach

Nontrivial merge: reintroduces the setNewStream method which was removed
in #2551 (I think it makes
sense as a convenient way to re-use the feed wrapper object but switch out
the feed? Comment updated appropriately.)