Get type safety in DI, fix character joiner not using buffer service

src/common/services/CoreService.ts

@@ -13,6 +13,8 @@ const DEFAULT_DEC_PRIVATE_MODES: IDecPrivateModes = Object.freeze({
 });
 
 export class CoreService implements ICoreService {
+  _serviceBrand: any;
+
   public decPrivateModes: IDecPrivateModes;
 
   private _onData = new EventEmitter<string>();