ocaml: Improve highlighting and bracketing

[lord]

Some small improvements to OCaml. Would happily split these into smaller changes, discard anything, etc.

Before:

After:

OCaml highlighting and bracketing improvements
- Fixed bug where < was automatically closed with >.
- Typing {| now automatically closes with |}
- Type variables are now colored with variable.special instead of variable.
- Argument names in function declarations and application are now colored with label instead of property, even if they are punned.
- [@@ and [% in macros are now colored as bracket punctuation to match the closing ], rather than colored as attribute

Release Notes:

• N/A

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[lord]

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