Upgrade the root dependencies and setup to use Node.js v20

[eason9487]

Changes proposed in this Pull Request:

Part of #108

This PR:

• Bump dependencies and regenerate package-lock.json for this repo with Node.js v20.
• Set minimum support for Node.js to ">=18", which align with the dependencies' minimum (@wordpress/scripts@27.7.0).
• Set .nvmrc to use Node.js v20.
• Fix eslint errors for the samples files.
• Update the "Publish Compat Checker package" workflow to use Node.js v20.

💡 These workflows depend on the release version, woocommerce/grow/<action_name>@actions-v1, so they will be upgraded after the @actions-v2 is published.

• .github/workflows/js-linting.yml
• .github/workflows/php-coding-standards.yml
• .github/workflows/run-qit-all.yml

Detailed test instructions:

1. JS linter
   • Use Node.js v20
   • npm install
   • npm run lint:js to see if the linter can be run and if the linting can pass
     • There may be some import/no-unresolved warnings. This kind of warnings can be ignore because the packages of sub-packages may not be installed.
   • Repeat this test with Node.js v18
2. Inspect the "Publish Compat Checker package" workflow
   • The current s0/git-publish-subdir-action@develop revision already uses Node.js v20
   • The last workflow run shows the following warning. The warning should be fixed after c8606e5
     

[eason9487]

I will be skipping the code review process as it can be optional for a devs-facing only change.