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/sqldelight/data/sources.sq

@@ -4,7 +4,11 @@ CREATE TABLE sources(
     name TEXT NOT NULL
 );
 
-getSourceData:
+findAll:
+SELECT *
+FROM sources;
+
+findOne:
 SELECT *
 FROM sources
 WHERE _id = :id;