chore: remove React 16.4's obsolete React imports

[hainenber]

chore: remove unused React imports

SUMMARY

React imports are no longer necessary starting from React 16.4.0 (source), I ran npx react-codemod update-react-imports. Afterwards, I executed this snippet to confirm everything stays intact

npm ci
npm run build
npm run test
npm run dev-server

Notable changes:

• Added ESLint configs as recommended per React doc
• Added Babel and Webpack configs to allow working with new automatic JSX runtime.
• Fix a build warning due to a type import misdirected as normal import.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

All CI should be green

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[hainenber]

Converting this to draft as there are weird behaviors after removal

[hainenber]

Phew! I've worked out all the edge cases and CI is green now, re-open for review :D

[michael-s-molina]

Thank you for the PR @hainenber. Can we add a lint rule to prevent unused React imports?

[hainenber]

I've added the lint rule as requested :D

[rusackas]

Appreciate the comments!

[hainenber]

I should clarify that I was unable to refactor the reactify.test.tsx to decouple it from whole React import :(

I hope someone much better than me can do the needful in the future.

[rusackas]

Trying to review this big of a PR is giving my browser a heart attack, and making my eyes bleed :P

I've reviewed about 700 of the files in a somewhat random order, and all looks good to me.

GitHub makes me "load diff" for the rest of the files, and it takes foreeeeeeeever. You would think filtering by file type or filtering out "viewed" files would help, but NOPE.