Update to React 19

[sanderdesnaijer]

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

[sanderdesnaijer]

Hi @nomcopter, friendly ping on this PR for React 19 support when you have time. Happy to make changes if needed.

[nomcopter]

Thanks for the PR! @Lonli-Lokli is working on merging his fork in in #240 which will include an update to React 19 and so we'll hold off for that to prevent conflicts

[sanderdesnaijer]

Allright thanks @nomcopter that sounds good!