refactored `modal.react.js` in `web` to use `lib` Modal component. All the removed code in this diff now lives in `lib/components/modal.react`
Next Steps:
# Refactor `modal-provider.js` imports in `web` to use `lib` instead of `web`
# Refacor `modal.react.js` in `landing`
# Refactor `modal-provider.js` imports in `landing` to use `lib` instead of `landing`
---
Depends on D5353
Linear Task: [[ https://linear.app/comm/issue/ENG-2038/refactor-modal-into-lib | ENG-2038 ]]