de-MSC-ifying space summaries (MSC2946) (#3134)

- This PR moves and refactors the
[code](https://github.com/matrix-org/dendrite/blob/main/setup/mscs/msc2946/msc2946.go)
for
[MSC2946](https://github.com/matrix-org/matrix-spec-proposals/pull/2946)
('Space Summaries') to integrate it into the rest of the codebase.
- Means space summaries are no longer hidden behind an MSC flag
- Solves #3096

Signed-off-by: Sam Wedgwood <sam@wedgwood.dev>

roomserver/roomserver_test.go

@@ -249,13 +249,14 @@ func TestPurgeRoom(t *testing.T) {
 		defer jetstream.DeleteAllStreams(jsCtx, &cfg.Global.JetStream)
 
 		rsAPI := roomserver.NewInternalAPI(processCtx, cfg, cm, &natsInstance, caches, caching.DisableMetrics)
-		userAPI := userapi.NewInternalAPI(processCtx, cfg, cm, &natsInstance, rsAPI, nil)
 
 		// this starts the JetStream consumers
-		syncapi.AddPublicRoutes(processCtx, routers, cfg, cm, &natsInstance, userAPI, rsAPI, caches, caching.DisableMetrics)
 		fsAPI := federationapi.NewInternalAPI(processCtx, cfg, cm, &natsInstance, nil, rsAPI, caches, nil, true)
 		rsAPI.SetFederationAPI(fsAPI, nil)
 
+		userAPI := userapi.NewInternalAPI(processCtx, cfg, cm, &natsInstance, rsAPI, nil)
+		syncapi.AddPublicRoutes(processCtx, routers, cfg, cm, &natsInstance, userAPI, rsAPI, caches, caching.DisableMetrics)
+
 		// Create the room
 		if err = api.SendEvents(ctx, rsAPI, api.KindNew, room.Events(), "test", "test", "test", nil, false); err != nil {
 			t.Fatalf("failed to send events: %v", err)
@@ -1035,8 +1036,8 @@ func TestUpgrade(t *testing.T) {
 		caches := caching.NewRistrettoCache(128*1024*1024, time.Hour, caching.DisableMetrics)
 
 		rsAPI := roomserver.NewInternalAPI(processCtx, cfg, cm, &natsInstance, caches, caching.DisableMetrics)
-		userAPI := userapi.NewInternalAPI(processCtx, cfg, cm, &natsInstance, rsAPI, nil)
 		rsAPI.SetFederationAPI(nil, nil)
+		userAPI := userapi.NewInternalAPI(processCtx, cfg, cm, &natsInstance, rsAPI, nil)
 		rsAPI.SetUserAPI(userAPI)
 
 		for _, tc := range testCases {