Fix function types used as type parameters

[tobil4sk]

This was broken previously:

var x:T<S -> R>;

As a side effect of the change, builtin types used as type parameters also highlight properly now:

var i:Null<Int>;

Previously the Int here was highlighted as @type, not @type.builtin.

I've also changed it so that when highlighting a type e.g. Null<S -> R>, it only highlights the type name (i.e. Null). Previously it would highlight the entire type Null<S -> R>, which meant that -> was also highlighted with @type.builtin.