Support new features (OCaml 4.12+)

[314eter]

• Hash sign in prefix operators (Add ppx-only unary operators ocaml/ocaml#9429)
• Let punning (Syntax proposal: let punning ocaml/ocaml#10013)
• Naming existentials in patterns (Allow to name existentials in pattern-matching ocaml/ocaml#9584)
• Module type substitutions (Module type substitutions ocaml/ocaml#10133)

[314eter]

The Github Actions tests don't run apparently, but they are failing: https://github.com/314eter/tree-sitter-ocaml/runs/1994780189

This is not related to changes in this PR, they were fine before I updated the examples in the last commit: https://github.com/314eter/tree-sitter-ocaml/runs/1994761493

With this (same) content in test.ml and test.mli, tree-sitter parse test.ml is fine but tree-sitter parse test.mli fails.

module type T = sig
  val f : ?x (**) : int -> int
end

This is really weird, since the ocaml and interface parsers are almost the same. The comment is parsed by an external scanner, which does return true, but tree-sitter acts like it returns false and then fails to parse the comment.

@maxbrunsfeld Is this a known bug in tree-sitter? It seems to be solved in tree-sitter 0.18.

[undu]

The Github Actions tests don't run apparently,

I think the branches field for the pull request should be removed, not sure why it's limited to some names

  pull_request:
    branches:
      - '**:**'

[314eter]

@undu That was indeed the problem, thanks.

[314eter]

I rebased this PR on master, and tree-sitter 0.19 fixes the failing tests.