dillon1000/react

Improve hydration fixture, support older versions of React (#14118)

* Hydration Fixture: Only load ReactDOMServer if it exists

Fixes an issue where the hydration fixture would try to load in
ReactDOMServer below version 14. In version 13, string markup methods
exist on the React namespace.

* DOM Fixtures: Use class component for App.js

This was breaking React 0.13.0.

* Hydration Fixture: better findDOMNode compatibility

This commit fixes an issue where the Hydration DOM fixture was
unusable in React 0.13.0 or lower because of newer API usage.

It fixes that by avoiding the use of refs to get the textarea
reference in the code editor component, using various versions of
findDOMNode as required.

* Hydration Fixture: Do not show dropdown for single-line errors

If an error showed for the hydration fixture, a detail element was
used even if no additional lines could display. In that case, this
commit changes the component such that it returns a div.

* Deeper React version support for hydration fixture

This commit adds support for versions 0.4.0 of React and higher for
the hydration fixture.

The DOM test fixtures themselves do not support down to React 0.4.0,
which would be exhaustive. Instead, the Hydration fixture can pick a
version to use for its own purposes. By default, this is the version
of React used by the fixtures.

In the process of doing this, I had to make some updates to the
renderer.html document associated with the hydration fixture, and I've
added some comments to better document the history of API changes.