Syntax highlighting for new Dune keywords. #1972
Description
There are a bunch of new keywords introduced in the ongoing work for supporting parameterised libraries in Dune. More details on the new additions are here: ocaml/dune#12111. I'm opening this to not forget to add syntax highlighting to the new keywords. I believe, and @voodoos agreed the update needs to happen here: https://github.com/ocamllabs/vscode-ocaml-platform/blob/master/syntaxes/dune.json.