Core: Improve performance of QUnit.equiv()

Small refactors (removals/adjustments) to make code more readable.
Makes code more readable and remove variable mutations.

* Remove IIFE closure, moving main function as direct export,
  and the rest as top-level local function.

* callbacks.object: Optimize compareConstructors().

* callbacks.object: Optimize object comparison prop call by skipping
  overhead and indirection of typeEquiv() for known array type.

* callbacks.array: Optimize isContainer() away, using a predefined Set.

* innerEquiv: Remove array allocation by re-using `slice` reference.

Closes #1700.

build/browserstack-quick.json

@@ -10,14 +10,6 @@
     "ie_9",
     "safari_9.1",
     "safari_current",
-    {
-
-      "browser": "opera",
-      "browser_version": "36.0",
-      "device": null,
-      "os": "OS X",
-      "os_version": "Sierra"
-    },
     "opera_current",
     "chrome_current",
     {

src/core/utilities.js

@@ -3,6 +3,7 @@ import Logger from '../logger';
 
 export const toString = Object.prototype.toString;
 export const hasOwn = Object.prototype.hasOwnProperty;
+export const slice = Array.prototype.slice;
 
 const nativePerf = getNativePerf();