QmlDesigner: Move item library entries to project storage

The subcomponent manager is synchronizing some meta files with the item
library. The project storage is synchronizing types. Synchronizing both
is quite complicated. Moving the the functionality to the project
storage removes that synchronization task.

Task-number: QDS-10266
Change-Id: Icdf14fbe85d5c4891542acae85ebecf0ba77b45d
Reviewed-by: Qt CI Patch Build Bot <ci_patchbuild_bot@qt.io>
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/libs/sqlite/sqlitedatabase.h

@@ -161,6 +161,9 @@ public:
     void sessionCommit() override;
     void sessionRollback() override;
 
+    void resetDatabaseForTestsOnly();
+    void clearAllTablesForTestsOnly();
+
 private:
     void initializeTables();
     void registerTransactionStatements();