Add rest loop position optimization fixture.

(Failing.)

With destructuring assignment to an element.

This makes the function ineligible for `arguments` optimization, while
remaining eligible for loop position optimization.

packages/babel-plugin-transform-es2015-parameters/test/fixtures/parameters/rest-deepest-common-ancestor-earliest-child/actual.js

@@ -1,4 +1,4 @@
-// single referenes
+// single reference
 function r(...rest){
   if (noNeedToWork) return 0;
   return rest;
@@ -66,3 +66,9 @@ function runQueue(queue, ...args) {
     }
   }
 }
+
+function r(...rest){
+  if (noNeedToWork) return 0;
+  [rest[0]] = x;
+  return rest;
+}

packages/babel-plugin-transform-es2015-parameters/test/fixtures/parameters/rest-deepest-common-ancestor-earliest-child/expected.js

@@ -1,4 +1,4 @@
-// single referenes
+// single reference
 function r() {
   if (noNeedToWork) return 0;
 
@@ -99,3 +99,19 @@ function runQueue(queue) {
     }
   }
 }
+
+function r() {
+  if (noNeedToWork) return 0;
+
+  for (var _len9 = arguments.length, rest = Array(_len9), _key9 = 0; _key9 < _len9; _key9++) {
+    rest[_key9] = arguments[_key9];
+  }
+
+  var _x = x;
+
+  var _x2 = babelHelpers.slicedToArray(_x, 1);
+
+  rest[0] = _x2[0];
+
+  return rest;
+}