fix where clauses in type aliases and allow empty where clauses (#259)

* parse where clauses in type identifiers before the =

* allow empty where clauses

* chore: tree-sitter generate

Author: m4rch3n1ng

grammar.js

@@ -425,6 +425,7 @@ module.exports = grammar({
       'type',
       field('name', $._type_identifier),
       field('type_parameters', optional($.type_parameters)),
+      optional($.where_clause),
       '=',
       field('type', $._type),
       optional($.where_clause),
@@ -465,8 +466,10 @@ module.exports = grammar({
 
     where_clause: $ => prec.right(seq(
       'where',
-      sepBy1(',', $.where_predicate),
-      optional(','),
+      optional(seq(
+        sepBy1(',', $.where_predicate),
+        optional(','),
+      )),
     )),
 
     where_predicate: $ => seq(