__curPos is not highlighted

[aciceri]

Notice that it's not a builtin but a keyword, I don't know where it should be added in the nil codebase. Also notice that probably there could be other keywords, it would be nice having a test or something that runs nix eval --expr "builtins.attrNames builtins" --json to check if we are considering all the builtins (if something similar isn't already done). I don't know if a similar introspection is possible also for keywords.