Update to React 19

#### Fixes #234 #### Changes proposed in this pull request: Updates React to 19 and the react-dnd-multi-backend to version 9. Updated packages: - react - react-dom - @types/react - @types/react-dom - react-dnd-multi-backend - core-js #### Reviewers should focus on: - should be able to run the tests `yarn test` - should be able to build `yarn build` #### Note Blueprint.js is not supporting React 19 at the moment, and probably wont in future for the current used version. Errors are shown in the ExampleApp but won't affect the build. The errors are muted by `client.overlay` inside the `webpack/hot.ts` file