upkeep/426: modernize developer experience

[Sidsector9]

All Submissions:

• [ ] Does your code follow the WooCommerce Sniffs variant of WordPress coding standards?
• [ ] Have you written new tests for your changes, as applicable?
• [ ] Have you successfully run tests with your changes locally?
• [ ] Will this change require new documentation or changes to existing documentation?

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Changes proposed in this Pull Request:

• Node is updated to v20.
• NPM is updated to v10.
• Node and NPM changes are reflected in the Github actions workflows.
• Build assets are generated by wordpress/scripts only.
• Entry point for all assets are moved under src/

Closes #426

Steps to test the changes in this Pull Request:

1. Pull the branch.
2. Run nvm use or nvm install depending on the situation.
3. Verify node and NPM versions by running node -v && npm -v.
4. rm -rf node_modules/.
5. npm ci && npm run build.
6. Test the plugin functionality.
7. Look for any 404 errors in console.
8. Look for any errors in the debug.log file.
9. Test the final ZIP.

E2E

Failing on 9.0.0-rc1 due to latest changes in block Checkout, need to update tetsts.

Passing on 8.9.1

Changelog entry

Dev - Update NPM packages and node version to v20 to modernize developer experience.

[vikrampm1]

@Sidsector9 is this ready for review?