Use Flow in ExtensionManager and SourceManager (#7547)

- Replace ExtensionManager relay and observable with Flow
- Inverse SourceManager dependency
    - SourceManager observers ExtensionManager flow
- Separate SourceData from SourceRepository as it created a circular dependency

app/src/main/java/eu/kanade/tachiyomi/AppModule.kt

@@ -87,10 +87,10 @@ class AppModule(val app: Application) : InjektModule {
 
         addSingletonFactory { NetworkHelper(app) }
 
-        addSingletonFactory { SourceManager(app).also { get<ExtensionManager>().init(it) } }
-
         addSingletonFactory { ExtensionManager(app) }
 
+        addSingletonFactory { SourceManager(app, get(), get()) }
+
         addSingletonFactory { DownloadManager(app) }
 
         addSingletonFactory { TrackManager(app) }