support list-initialization in an assignment expression

[hokein]

Example:

 void test(int a) {
// tree-sitter output is
//   expression_statement [1, 3] - [1, 10])
//        compound_literal_expression [1, 3] - [1, 9])
//          type: type_identifier [1, 3] - [1, 4])
//          ERROR [1, 5] - [1, 6])
//          value: initializer_list [1, 7] - [1, 9])  
   a = {};
}

Looks like this is not handled in the grammar.