There's been reports of syntax documentation sometimes spuriously showing hints about [@nontail] attributes. It turns out this was due to a ppx generating [@nontail] attributes whose location was ghost but encloses the cursor. The fix here is easy - we shouldn't be displaying syntax doc hints about nodes that are ghost.

Unforunately this is a difficult PR to write a test for. Writing a test would involve writing a ppx that generates ghost nodes, which would be a substantial amount of effort (partially because we wouldn't have ppxlib at our disposal to do so). Rather, I performed manual testing to verify that this fixes the reported errors.