All doc updates forv15.5 (#9359)

* `react-addons-test-utils` -> `react-dom/test-utils` Updating all references and docs on the `React.addons.TestUtils` and the shallow renderer to refer to the correct targets. Instead of: ``` const React = require('react'); // ... React.addons.Testutils // or const ReactTestUtils = require('react-addons-test-utils'); ``` we now show: ``` const ReactTestUtils = require('react-dom/test-utils'); ``` And for shallow renderer, instead of: ``` const shallowRenderer = TestUtils.createRenderer(); ``` we now show: ``` const shallowRenderer = require('react-test-renderer/shallow'); ``` * Update the 'prev' and 'next' attributes of 'add-ons' docs These flags are used to set arrow links to easily navigate through the documents. They were wrong or missing in some of the 'add-ons' pages and this bothered me when manually testing the updates from the previous commit. * Update syntax for instantiating shallow renderer Missed this when updating the docs for the changes to shallow-renderer in React 15.5. * Fix pointers in addons docs Thanks @bvaughn for catching this * Make example of shallow renderer more consistent We should show using the same variable names between code samples. * Make names in example even more consistent We should use the same variable name for the same thing across examples. `renderer` -> `shallowRenderer`. * Update docs to deprecate React<CSS>TransitionGroup - removes link to the docs about `ReactCSSTransitionGroup` and `ReactTransitionGroup` from the main navigation - updates 'prev' and 'next' pointers to skip this page - adds deprecation warning to the top of the page - remove references to these modules from the packages README - updates 'add-ons' main page to list this as a deprecated add-on * Update `React.createClass` to `createReactClass` in the docs The `React.createClass` method is being deprecated in favor of `createReactClass`. * Remove 'React.createClass' from top level API docs It no longer makes sense to have a section for the 'createClass' method in this page, since it won't be available as a top level method on 'React'. I initially was going to pull the section about 'createClass' into a separate page to add under 'addons' but it was short and duplicative of the 'react-without-es6' docs. So I just linked to those. * Remove *most* `React.PropTypes` from the docs I am doing the docs for `context` in a separate commit because that case was a bit less clear-cut. We will no longer support `React.PropTypes` as a built-in feature of React, and instead should direct folks to use the `PropTypes` project that stands alone. Rather than retaining the `React.PropTypes` examples and just revamping them to show the use of the stand-alone `PropTypes` library with React, it makes more sense to direct people to that project and reduce the perceived API area and complexity of React core. The proper place to document `PropTypes` is in the README or docs of that project, not in React docs. * Update `context` docs to not use `React.PropTypes` We use `React.PropTypes` to define the `contextType` for the `context` feature of React. It's unclear how this will work once `React.PropTypes` is replaced by the external `PropTypes` library. Some options; a) Deprecate `context`, either in v16 or shortly after. Seems reasonable based on the intense warnings against using context that we have in the docs - https://facebook.github.io/react/docs/context.html#why-not-to-use-context **Except** that probably some widely used libraries depend on it, like `React-Router`. b) Expect users will use external `PropTypes` library when defining `contextTypes` and just don't do our `checkReactTypeSpec` against them any more in v16. c) Stop masking context and pass the whole context unmasked everywhere. Worst option, do not recommend. I went with `b` and assume that, for now, we will get users to use the external `PropTypes` when defining context. I will update this PR if we want a different approach. * Remove 'addons' items from left nav, and deprecate 'addons' doc page The plan: [X] Remove links to 'addons' items from main navigation [X] Add deprecation notices where appropriate, and update syntax to show using the separate modules. [ ] Update other references to 'React.addons' in docs. Coming in next commit. --- blocked but coming in future PRs [ ] Link to a blog post describing the new locations of add-ons in the deprecation notice on the '/docs/addons.html' page. Blocked until we actually publish that blog post. [ ] Move the docs for each add-on to the actual github repo where it now lives. [ ] Redirect the old add-ons doc permalinks to the docs in the separate github repos for those modules. [ ] Remove the old add-ons doc markdown files from React core docs. * Remove references to `React.addons` from docs Just misc. places where we referenced the 'addons' feature. All gone!