Fix ts and dependency issues

[martimalek]

What:

Fixes TS issues that made the build fail and dependency conflicts that forced the install with the --legacy-peer-deps flag (except a conflict with react-tether, which will be solved separately).

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Why:

To have a working build and cleaner deps.

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How:

• To fix the build
  • Import missing theme in InfoBanner.tsx
  • Add necessary casts in BoxedInput.tsx
• To (almost) fix the deps conflicts
  • Migrate from @testing-library/react-hooks to @testing-library/react (the same APIs are now exposed from @testing-library/react so the former is not needed anymore)
  • Remove unused theme-ui package
  • Bump ts-jest from ^25.2.1 to ^26.5.6
  • Bump react-windowed-select from ^4.0.0 to ^5.1.0

Checklist:

• Check react-tether TS issue in pipeline
• Ready to be merged

After this PR the build issues are fixed and the only remaining dependency conflict is with react-tether, which will be removed from the project in favour of react-popper in #232

Relates to #232
Relates to #366 (will be closed together with #232)

[martimalek]

I tried bumping react-tether to 3.x.x but there are some TS issues that didn't seem easy to solve, IMO we should directly tackle #232

[github-actions]

🎉 This PR is included in version 3.0.0-next.1 🎉

The release is available on:

• npm package (@next dist-tag)
• GitHub release

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