Simplified Sliding Sync (#28515)

* Experimental SSS

Working branch to get SSS functional on element-web.

Requires https://github.com/matrix-org/matrix-js-sdk/pull/4400

* Adjust tests to use new behaviour

* Remove well-known proxy URL lookup; always use native

This is actually required for SSS because otherwise it would use
the proxy over native support.

* Linting

* Debug logging

* Control the race condition when swapping between rooms

* Dont' filter by space as synapse doesn't support it

* Remove SS code related to registering lists and managing ranges

- Update the spidering code to spider all the relevant lists.
- Add canonical alias to the required_state to allow room name calcs to work.

Room sort order is busted because we don't yet look at `bump_stamp`.

* User bumpStamp if it is present

* Drop initial room load from 20 per list to 10

* Half the batch size to trickle more quickly

* Prettier

* prettier on tests too

* Remove proxy URL & unused import

* Hopefully fix tests to assert what the behaviour is supposed to be

* Move the singleton to the manager tyo fix import loop

* Very well, code, I will remove you

Why were you there in the first place?

* Strip out more unused stuff

* Fix playwright test

Seems like this lack of order updating unless a room is selected
was just always a bug with both regular and non-sliding sync. I
have no idea how the test passed on develop because it won't run.

* Fix test to do maybe what it was supposed to do... possibly?

* Remove test for old pre-simplified sliding sync behaviour

* Unused import

* Remove sliding sync proxy & test

I was wrong about what this test was asserting, it was suposed
to assert that notification dots aren't shown (because SS didn't
support them somehow I guess) but they are fine in SSS so the test
is just no longer relevant.

* Remove now pointless credentials

* Remove subscription removal as SSS doesn't do that

* Update tests

* add test

* Switch to new labs flag & break if old labs flag is enabled

* Remove unused import & fix test

* Fix other test

* Remove name & description from old labs flag

as they're not displayed anywhere so not useful

* Remove old sliding sync option

by making it not a feature

* Add back unread nindicator test but inverted

and minus the bit about disabling notification which surely would have
defeated the original point anyway?

* Reinstate test for room_subscriptions

...and also make tests actually use sliding sync

* Use UserFriendlyError

* Remove empty constructor

* Remove unrelated changes

* Unused import

* Fix import

* Avoid moving import

---------

Co-authored-by: Kegan Dougal <7190048+kegsay@users.noreply.github.com>

test/unit-tests/stores/RoomViewStore-test.ts

@@ -383,43 +383,35 @@ describe("RoomViewStore", function () {
     describe("Sliding Sync", function () {
         beforeEach(() => {
             jest.spyOn(SettingsStore, "getValue").mockImplementation((settingName, roomId, value) => {
-                return settingName === "feature_sliding_sync"; // this is enabled, everything else is disabled.
+                return settingName === "feature_simplified_sliding_sync"; // this is enabled, everything else is disabled.
             });
         });
 
         it("subscribes to the room", async () => {
-            const setRoomVisible = jest
-                .spyOn(slidingSyncManager, "setRoomVisible")
-                .mockReturnValue(Promise.resolve(""));
+            const setRoomVisible = jest.spyOn(slidingSyncManager, "setRoomVisible").mockReturnValue(Promise.resolve());
             const subscribedRoomId = "!sub1:localhost";
             dis.dispatch({ action: Action.ViewRoom, room_id: subscribedRoomId });
             await untilDispatch(Action.ActiveRoomChanged, dis);
             expect(roomViewStore.getRoomId()).toBe(subscribedRoomId);
-            expect(setRoomVisible).toHaveBeenCalledWith(subscribedRoomId, true);
+            expect(setRoomVisible).toHaveBeenCalledWith(subscribedRoomId);
         });
 
-        // Regression test for an in-the-wild bug where rooms would rapidly switch forever in sliding sync mode
+        // Previously a regression test for an in-the-wild bug where rooms would rapidly switch forever in sliding sync mode
+        // although that was before the complexity was removed with similified mode. I've removed the complexity but kept the
+        // test anyway.
         it("doesn't get stuck in a loop if you view rooms quickly", async () => {
-            const setRoomVisible = jest
-                .spyOn(slidingSyncManager, "setRoomVisible")
-                .mockReturnValue(Promise.resolve(""));
+            const setRoomVisible = jest.spyOn(slidingSyncManager, "setRoomVisible").mockReturnValue(Promise.resolve());
             const subscribedRoomId = "!sub1:localhost";
             const subscribedRoomId2 = "!sub2:localhost";
             dis.dispatch({ action: Action.ViewRoom, room_id: subscribedRoomId }, true);
             dis.dispatch({ action: Action.ViewRoom, room_id: subscribedRoomId2 }, true);
             await untilDispatch(Action.ActiveRoomChanged, dis);
-            // sub(1) then unsub(1) sub(2), unsub(1)
-            const wantCalls = [
-                [subscribedRoomId, true],
-                [subscribedRoomId, false],
-                [subscribedRoomId2, true],
-                [subscribedRoomId, false],
-            ];
+            // should view 1, then 2
+            const wantCalls = [[subscribedRoomId], [subscribedRoomId2]];
             expect(setRoomVisible).toHaveBeenCalledTimes(wantCalls.length);
             wantCalls.forEach((v, i) => {
                 try {
                     expect(setRoomVisible.mock.calls[i][0]).toEqual(v[0]);
-                    expect(setRoomVisible.mock.calls[i][1]).toEqual(v[1]);
                 } catch {
                     throw new Error(`i=${i} got ${setRoomVisible.mock.calls[i]} want ${v}`);
                 }