Update to core v3.0.0-rc5 and sync v2.0.0-rc15.
Update to core v3.0.0-rc5 and sync v2.0.0-rc15.

realm/realm-object-store,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-object-store,realm/realm-object-store,realm/realm-core