Allow AST_DefaultAssign as parameter (#1778)

This may be the case for parsing arrow functions,
as left side expressions are converted to destructuring patterns
before being converted to parameters.

test/compress/harmony.js

@@ -314,13 +314,25 @@ default_assign: {
         function f(a, b = 3) {
             console.log(a);
         }
+
         g = ([[] = 123]) => {};
+        h = ([[x, y, z] = [4, 5, 6]] = []) => {};
+
+        function i([[x, y, z] = [4, 5, 6]] = []) {
+            console.log(b);
+        };
     }
     expect: {
         function f(a) {
             console.log(a);
         }
+
         g = ([[] = 123]) => {};
+        h = ([[x, y, z] = [4, 5, 6]] = []) => {};
+
+        function i([[x, y, z] = [4, 5, 6]] = []) {
+            console.log(b);
+        };
     }
 }