Support MSC4222 state_after (#4487)

* WIP support for state_after

* Fix sliding sync sdk / embedded tests

* Allow both state & state_after to be undefined

Since it must have allowed state to be undefined previously: the test
had it as such.

* Fix limited sync handling

* Need to use state_after being undefined

if state can be undefined anyway

* Make sliding sync sdk tests pass

* Remove deprecated interfaces & backwards-compat code

* Remove useless assignment

* Use updates unstable prefix

* Clarify docs

* Remove additional semi-backwards compatible overload

* Update unstable prefixes

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Fix test

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add test for MSC4222 behaviour

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Improve coverage

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Fix tests

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Tidy

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add comments to explain why things work as they are.

* Fix sync accumulator for state_after sync handling

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add tests

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Revert "Fix room state being updated with old (now overwritten) state and emitting for those updates. (#4242)"

This reverts commit 957329b218.

* Fix Sync Accumulator toJSON putting start timeline state in state_after field

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Update tests

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add test case

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Iterate

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

---------

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>
Co-authored-by: Hugh Nimmo-Smith <hughns@matrix.org>
Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>
Co-authored-by: Timo <toger5@hotmail.de>

spec/integ/sliding-sync-sdk.spec.ts

@@ -601,13 +601,13 @@ describe("SlidingSyncSdk", () => {
             mockSlidingSync!.emit(SlidingSyncEvent.RoomData, roomId, {
                 initial: true,
                 name: "Room with Invite",
-                required_state: [],
-                timeline: [
+                required_state: [
                     mkOwnStateEvent(EventType.RoomCreate, {}, ""),
                     mkOwnStateEvent(EventType.RoomMember, { membership: KnownMembership.Join }, selfUserId),
                     mkOwnStateEvent(EventType.RoomPowerLevels, { users: { [selfUserId]: 100 } }, ""),
                     mkOwnStateEvent(EventType.RoomMember, { membership: KnownMembership.Invite }, invitee),
                 ],
+                timeline: [],
             });
             await httpBackend!.flush("/profile", 1, 1000);
             await emitPromise(client!, RoomMemberEvent.Name);
@@ -921,13 +921,12 @@ describe("SlidingSyncSdk", () => {
             const roomId = "!room:id";
             mockSlidingSync!.emit(SlidingSyncEvent.RoomData, roomId, {
                 name: "Room with typing",
-                required_state: [],
-                timeline: [
+                required_state: [
                     mkOwnStateEvent(EventType.RoomCreate, {}, ""),
                     mkOwnStateEvent(EventType.RoomMember, { membership: KnownMembership.Join }, selfUserId),
                     mkOwnStateEvent(EventType.RoomPowerLevels, { users: { [selfUserId]: 100 } }, ""),
-                    mkOwnEvent(EventType.RoomMessage, { body: "hello" }),
                 ],
+                timeline: [mkOwnEvent(EventType.RoomMessage, { body: "hello" })],
                 initial: true,
             });
             await emitPromise(client!, ClientEvent.Room);
@@ -962,13 +961,12 @@ describe("SlidingSyncSdk", () => {
             const roomId = "!room:id";
             mockSlidingSync!.emit(SlidingSyncEvent.RoomData, roomId, {
                 name: "Room with typing",
-                required_state: [],
-                timeline: [
+                required_state: [
                     mkOwnStateEvent(EventType.RoomCreate, {}, ""),
                     mkOwnStateEvent(EventType.RoomMember, { membership: KnownMembership.Join }, selfUserId),
                     mkOwnStateEvent(EventType.RoomPowerLevels, { users: { [selfUserId]: 100 } }, ""),
-                    mkOwnEvent(EventType.RoomMessage, { body: "hello" }),
                 ],
+                timeline: [mkOwnEvent(EventType.RoomMessage, { body: "hello" })],
                 initial: true,
             });
             const room = client!.getRoom(roomId)!;