Add JS Tests Workflow and Fix JS Unit tests

[puntope]

Description

• Refactor and clean JS tests after PayPal Payment methods refactor performed in Fix disabled functionality for Save PayPal and Venmo (PCP-4489) #3650
• Add JS Tests Workflow running when PR happens and includes JS files
• Fix other errors from Unit tests
• Updated docs
• Added tests coverage mode

Steps to Test

1. Run npm run test:unit-js
2. Tests pass
3. Run in coverage mode npm run test:unit-js:coverage
4. Tests make sense and cover current scenarios
5. See JS Unit tests successfully passing in Workflow

[github-actions]

Test using WordPress Playground

The changes in this pull request can be previewed and tested using a WordPress Playground instance.
WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

🔗 Test this pull request with WordPress Playground

What's included:

• ✅ WordPress (latest)
• ✅ WooCommerce (latest)
• ✅ PayPal Payments plugin v3.3.0-pr3902-19898593376-gc5c5858 (built from this PR)

Login credentials:

• Username: admin
• Password: password

Plugin Details:

• Version: 3.3.0-pr3902-19898593376-gc5c5858
• Commit: c5c5858
• Artifact: woocommerce-paypal-payments-3.3.0-pr3902-19898593376-gc5c5858

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_{🤖 Auto-generated for commit c5c5858 • Last updated: 2025-12-03T15:17:31.149Z}