Add failing test case for object rest after array rest, and fix it. (#6213)

* Add failing test case for object rest after array rest.

Discovered while upgrading https://github.com/meteor/babel to Babel 7.

The error is:

  1) babel-plugin-transform-object-rest-spread/object rest with array rest:
     TypeError: /Users/ben/dev/babel/packages/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/with-array-rest/actual.js: Property id of VariableDeclarator expected node to be of a type ["LVal"] but instead got null
      at Object.validate (packages/babel-types/lib/definitions/index.js:73:13)
      at validate (packages/babel-types/lib/index.js:460:9)
      at Object.builder (packages/babel-types/lib/index.js:428:7)
      at Object.RestElement (packages/babel-plugin-transform-object-rest-spread/lib/index.js:157:41)
      at NodePath._call (packages/babel-traverse/lib/path/context.js:53:20)
      at NodePath.call (packages/babel-traverse/lib/path/context.js:40:17)
      at NodePath.visit (packages/babel-traverse/lib/path/context.js:84:12)
      ...

* Fix object rest following array rest. (#6213)

* Avoid treating array ...rest elements as object ...rest properties.

* Also avoid treating ...rest parameters as object ...rest properties.

Returning early if the parent was an ArrayPattern was not quite enough,
since a RestElement can appear as a parameter in a Function as well.

* Move RestElement parent check earlier in visitor method.

packages/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/with-array-rest/actual.js

@@ -0,0 +1,8 @@
+let {
+  a: [b, ...arrayRest],
+  c = function(...functionRest){},
+  ...objectRest
+} = {
+  a: [1, 2, 3, 4],
+  d: "oyez"
+};

packages/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/with-array-rest/expected.js

@@ -0,0 +1,9 @@
+let _a$d = {
+  a: [1, 2, 3, 4],
+  d: "oyez"
+},
+    {
+  a: [b, ...arrayRest],
+  c = function (...functionRest) {}
+} = _a$d,
+    objectRest = babelHelpers.objectWithoutProperties(_a$d, ["a", "c"]);