Preparations for removing BaseDendrite (#3016)

Preparations to actually remove/replace `BaseDendrite`.
Quite a few changes:
- SyncAPI accepts an `fulltext.Indexer` interface (fulltext is removed
from `BaseDendrite`)
- Caches are removed from `BaseDendrite`
- Introduces a `Router` struct (likely to change)
  - also fixes #2903
- Introduces a `sqlutil.ConnectionManager`, which should remove
`base.DatabaseConnection` later on
- probably more

federationapi/routing/profile_test.go

@@ -50,7 +50,7 @@ func TestHandleQueryProfile(t *testing.T) {
 		defer close()
 
 		fedMux := mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicFederationPathPrefix).Subrouter().UseEncodedPath()
-		base.PublicFederationAPIMux = fedMux
+		base.Routers.Federation = fedMux
 		base.Cfg.FederationAPI.Matrix.SigningIdentity.ServerName = testOrigin
 		base.Cfg.FederationAPI.Matrix.Metrics.Enabled = false
 		fedClient := fakeFedClient{}

federationapi/routing/query_test.go

@@ -50,7 +50,7 @@ func TestHandleQueryDirectory(t *testing.T) {
 		defer close()
 
 		fedMux := mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicFederationPathPrefix).Subrouter().UseEncodedPath()
-		base.PublicFederationAPIMux = fedMux
+		base.Routers.Federation = fedMux
 		base.Cfg.FederationAPI.Matrix.SigningIdentity.ServerName = testOrigin
 		base.Cfg.FederationAPI.Matrix.Metrics.Enabled = false
 		fedClient := fakeFedClient{}

federationapi/routing/routing.go

@@ -65,9 +65,9 @@ func Setup(
 	servers federationAPI.ServersInRoomProvider,
 	producer *producers.SyncAPIProducer,
 ) {
-	fedMux := base.PublicFederationAPIMux
-	keyMux := base.PublicKeyAPIMux
-	wkMux := base.PublicWellKnownAPIMux
+	fedMux := base.Routers.Federation
+	keyMux := base.Routers.Keys
+	wkMux := base.Routers.WellKnown
 	cfg := &base.Cfg.FederationAPI
 
 	if base.EnableMetrics {

federationapi/routing/send_test.go

@@ -48,7 +48,7 @@ func TestHandleSend(t *testing.T) {
 		defer close()
 
 		fedMux := mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicFederationPathPrefix).Subrouter().UseEncodedPath()
-		base.PublicFederationAPIMux = fedMux
+		base.Routers.Federation = fedMux
 		base.Cfg.FederationAPI.Matrix.SigningIdentity.ServerName = testOrigin
 		base.Cfg.FederationAPI.Matrix.Metrics.Enabled = false
 		fedapi := fedAPI.NewInternalAPI(base, nil, nil, nil, nil, true)