Add changelog for 18.3 (#28929)

Fixes #28924

CHANGELOG.md

@@ -1,3 +1,24 @@
+## 18.3.0 (April 25, 2024)
+
+This release is identical to 18.2 but adds warnings for deprecated APIs and other changes that are needed for React 19.
+
+Read the [React 19 Upgrade Guide](https://react.dev/blog/2024/04/25/react-19-upgrade-guide) for more info.
+
+### React
+
+- Allow writing to `this.refs` to support string ref codemod [909071](https://github.com/facebook/react/commit/9090712fd3ca4e1099e1f92e67933c2cb4f32552)
+- Warn for deprecated `findDOMNode` outside StrictMode [c3b283](https://github.com/facebook/react/commit/c3b283964108b0e8dbcf1f9eb2e7e67815e39dfb)
+- Warn for deprecated `test-utils` methods [d4ea75](https://github.com/facebook/react/commit/d4ea75dc4258095593b6ac764289f42bddeb835c)
+- Warn for deprecated Legacy Context outside StrictMode [415ee0](https://github.com/facebook/react/commit/415ee0e6ea0fe3e288e65868df2e3241143d5f7f)
+- Warn for deprecated string refs outside StrictMode [#25383](https://github.com/facebook/react/pull/25383)
+- Warn for deprecated `defaultProps` for function components [#25699](https://github.com/facebook/react/pull/25699)
+- Warn when spreading `key` [#25697](https://github.com/facebook/react/pull/25697)
+- Warn when using `act` from `test-utils` [d4ea75](https://github.com/facebook/react/commit/d4ea75dc4258095593b6ac764289f42bddeb835c)
+
+### React DOM
+- Warn for deprecated `unmountComponentAtNode` [8a015b](https://github.com/facebook/react/commit/8a015b68cc060079878e426610e64e86fb328f8d)
+- Warn for deprecated `renderToStaticNodeStream` [#28874](https://github.com/facebook/react/pull/28874)
+
 ## 18.2.0 (June 14, 2022)
 
 ### React DOM