addEntry(entry) {
    const persistentChildCompilerSingletonPlugin = compilerMap.get(
      this.compiler,
    );
    if (!persistentChildCompilerSingletonPlugin) {
      throw new Error(
        "PersistentChildCompilerSingletonPlugin instance not found.",
      );
    }
    persistentChildCompilerSingletonPlugin.addEntry(entry);
  }
apply is called by the webpack main compiler during the start phase
@param {string} entry