Dependabot Security Related Fixes & Refactoring

[timnolte]

All Submissions:

• Have you followed the plugin Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

• Update to require Node v14 & NPM 6.14.15.
• Updates to Grunt 1.4.1.
• Forces resolution of dependencies for security fixes.
• Update @WordPress packages to their latest versions.
• Refactors the NPM & Composer scripts.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

• Fixes open Dependabot security advisories.
• Refactors development environment NPM & Composer scripts.