Add support for nominal types

Summary:
Add support for nominal type aliases as per [EEP-69](https://github.com/erlang/eep/blob/master/eeps/eep-0069.md).

Note: this updates the grammar only, matching ELP changes will follow

Reviewed By: ilya-klyuchnikov

Differential Revision: D72445312

fbshipit-source-id: 47aebda7e99c7bd2b3033642a01ed06cc9dbd633

Author: alanz

grammar.js

@@ -237,6 +237,7 @@ module.exports = grammar({
             $.deprecated_attribute,
             $.record_decl,
             $.type_alias,
+            $.nominal,
             $.opaque,
             $.spec,
             $.callback,
@@ -437,6 +438,8 @@ module.exports = grammar({
 
         type_alias: $ => seq('-', atom_const('type'), $._type_def, '.'),
 
+        nominal: $ => seq('-', atom_const('nominal'), $._type_def, '.'),
+
         opaque: $ => seq('-', atom_const('opaque'), $._type_def, '.'),
 
         _type_def: $ => choice(