Add the OCaml problem matchers

[avsm]

Can probably get these from the VSCode plugin, but need to check that they work with the OCaml 4.08+ new error message format.

[smorimoto]

It's actually possible to do that with a few hacks, but I think the user will have to choose which matcher to add. This is because if you're using something such as dune, you might need some additional configuration for it: https://github.com/ocamllabs/vscode-ocaml-platform/issues/227#issuecomment-633099912

[smorimoto]

Blocked by: https://github.com/actions/toolkit/issues/1540