Remove Yarn and replace it with corresponding npm features

[bryanbraun]

This will include:

• Removing the Yarn dependency from package.json.
• Generating a package.lock file to replace the yarn.lock file.
  • This may create some patch/minor update, so we'll need to check to see that the site is still working as expected.
• Updating references to Yarn in the docs, like here and here.
• Replacing any other uses of Yarn in the codebase.