chore: convert repo from yarn to npm

[MikeMcC399]

Issue

The repo contains a committed yarn.lock from the Yarn v1 Classic package manager. Yarn v1 is however frozen and no longer actively supported.

Background

Yarn v1 Classic entered maintenance mode in January 2020, more than 4 years ago, as noted on the Installation documentation page. The GitHub repo https://github.com/yarnpkg/yarn shows the message

The 1.x line is frozen - features and bugfixes now happen on https://github.com/yarnpkg/berry".

CircleCI is the only CI workflow in use and it does not use Yarn in its circle.yml workflow file.

package.json now contains only markdown-link-check and prettier in devDependencies. (The corresponding scripts are dormant and fail if invoked. They could potentially be revived at a later stage.)

Changes

Replace the yarn.lock from Yarn v1 Classic with a package-lock.json for use with npm instead of Yarn.

[cypress-app-bot]

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