Coalesce warnings for deprecated lifecycle hooks and print single message after reconciliation (rather than one per component-type).

Relates to PR #12028 and [this comment](https://github.com/facebook/react/pull/12028#discussion_r162420575).
this.log('componentWillMount');
      },
      componentDidMount() {
        this.log('componentDidMount');
      },
      componentWillUpdate() {
        this.log('componentWillUpdate');
      },
      componentDidUpdate() {
        this.log('componentDidUpdate');
      },
      componentWillUnmount() {
        this.log('componentWillUnmount');
      },
      render() {
        instance = this;
        this.log('render');
        return <div />;
      },
    });
    const container = document.createElement('div');
    
    
    
    
    
    
    expect(() => ReactDOM.render(<Component />, container)).toWarnDev([
      'Warning: MyComponent: isMounted is deprecated. Instead, make sure to ' +