Standalone command-line option to typecheck a .sw file

[byorgey]

We have swarm format, and we have the LSP, but sometimes it might be nice to have a quick command-line-friendly way to fully parse + typecheck a .sw file. Concretely, I propose adding a new subcommand swarm check which is similar to swarm format but also typechecks the indicated file, and prints any errors (or a brief "OK" message) to stdout.

[kostmo]

That would be nice. FYI there does currently exist a webserver-dependent option introduced in #1142:

curl --silent -H "Content-Type: text/plain; charset=utf-8"  -i http://localhost:5357/code/render --data @data/test/language-snippets/warnings/unused-vars/multiple-lambda-first-unused.sw