Tooling updates, types and removing unneeded files from the published package

[BPScott]

Updating a few tooling things:

• Change package manager: Switch yarn v1 to pnpm
• Change test runner: Switch mocha to using node's built-in test runner
• Use latest versions of eslint and prettier
• Move dependabot config into .github and make it group updates
• Add Actions workflow for running tests and linting

Two package changes:

• Add types in index.d.ts
• Add files array in package.json so the published package only includes the index.{js,d.ts} files