That is somewhat above my pay grade, so to speak, but I imagine that you would need to write a plugin that talks to a language server (I think this is true for Code and other LSP-aware editors, too). You'd probably start by checking "show extension development items in the Extensions menu," then select "Create New Extension..." in that menu and choose "Language Server Extension" in the pane that comes up next. That looks like it creates a skeleton extension for you with the basic details filled in.
