Add support for svelte-check

[spenserblack]

Name: svelte-check URL: https://www.npmjs.com/package/svelte-check, https://github.com/sveltejs/language-tools/tree/master/packages/svelte-check

svelte-check is a tool that can be used to find issues with .svelte files, such as unused CSS or Typescript errors. Machine-readable output is possible with svelte-check --output machine.