fix: date-fns import and esm output for react-core

[connorlindsey]

1. Fixes dependencies by moving zustand and date-fns to react-core
2. Adds babel-plugin-date-fns for compatibility with @knocklabs/react-notification-feed
3. Updates react-core to output .js files for the esm build and updates the exports to fix an issue with Webpack 5. Before these changes, using the react packages in a CRA app would cause the following error:

BREAKING CHANGE: The request 'date-fns/locale' failed to resolve only because it was resolved as fully specified
(probably because the origin is strict EcmaScript Module, e. g. a module with javascript mimetype, a '*.mjs' file, or a '*.js' file where the package.json contains '"type": "module"').
The extension in the request is mandatory for it to be fully specified.
Add the extension to the request.

For some background, here's an example of the same issue in React Spring: pmndrs/react-spring#2101

[linear]

KNO-4992 Fix date-fns/locale import issue

Affects CRA using knocklabs/react

Module not found: Error: Can't resolve 'date-fns/locale' in '/Users/connor/Dev/knock/test/cra-install-test/node_modules/knocklabs/react-core/dist/esm/modules/core/context'
Did you mean 'index.js'?
BREAKING CHANGE: The request 'date-fns/locale' failed to resolve only because it was resolved as fully specified
(probably because the origin is strict EcmaScript Module, e. g. a module with javascript mimetype, a '*.mjs' file, or a '*.js' file where the package.json contains '"type": "module"').
The extension in the request is mandatory for it to be fully specified.
Add the extension to the request.

react-notification-feed uses "babel-plugin-date-fns"

[changeset-bot]

🦋 Changeset detected

Latest commit: 1af536b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@knocklabs/react-core	Patch
@knocklabs/react	Patch
nextjs-example	Patch

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[cjbell]

🖖