Build: Move /src/core/diff.js to /src/diff.js

This produces strings (HTML) and is available unconditionally.
It does not depend on the DOM.

Pluck its test out of /test/reporter-html/ and add it to /test/main
instead. Thus coverering it in Node.js, mozjs, web worker,
and CLI as well.

Ref #1726.

Gruntfile.js

@@ -125,6 +125,7 @@ module.exports = function (grunt) {
         'test/main/assert-timeout.js',
         'test/main/async.js',
         'test/main/deepEqual.js',
+        'test/main/diff.js',
         'test/main/dump.js',
         'test/main/each.js',
         'test/main/modules.js',

src/core.js

@@ -18,7 +18,7 @@ import ProcessingQueue from './core/processing-queue';
 import { urlParams } from './urlparams';
 import { on, emit } from './events';
 import onUncaughtException from './core/on-uncaught-exception';
-import diff from './core/diff';
+import diff from './diff';
 
 const QUnit = {};
 

src/core/diff.js → src/diff.js

@@ -1,5 +1,5 @@
 /* eslint-disable indent */
-import { escapeText } from '../core/utilities';
+import { escapeText } from './core/utilities';
 
 /*
  * This file is a modified version of google-diff-match-patch's JavaScript implementation

src/reporters/HtmlReporter.js

@@ -1,5 +1,5 @@
 import { extend, errorString, escapeText } from '../core/utilities';
-import diff from '../core/diff';
+import diff from '../diff';
 import dump from '../dump';
 import { window, document, navigator, StringMap } from '../globals';
 import { urlParams } from '../urlparams';

test/index.html

@@ -15,6 +15,7 @@
   <script src="main/assert-timeout.js"></script>
   <script src="main/async.js"></script>
   <script src="main/deepEqual.js"></script>
+  <script src="main/diff.js"></script>
   <script src="main/dump.js"></script>
   <script src="main/each.js"></script>
   <script src="main/modules.js"></script>
@@ -25,7 +26,6 @@
   <script src="main/test.js"></script>
   <script src="main/utilities.js"></script>
 
-  <script src="reporter-html/diff.js"></script>
   <script src="reporter-html/reporter-html.js"></script>
   <script src="reporter-html/unhandled-rejection.js"></script>
 </head>

test/mozjs.js

@@ -17,6 +17,7 @@ loadRelativeToScript('../test/main/assert-step.js');
 // loadRelativeToScript( "../test/main/assert-timeout.js" ); // Requires setTimeout
 // loadRelativeToScript( "../test/main/async.js" ); // Requires setTimeout
 loadRelativeToScript('../test/main/deepEqual.js');
+loadRelativeToScript('../test/main/diff.js');
 loadRelativeToScript('../test/main/dump.js');
 loadRelativeToScript('../test/main/each.js');
 // loadRelativeToScript( "../test/main/modules.js" ); // Requires setTimeout

test/webWorker-worker.js

@@ -11,6 +11,7 @@ importScripts(
   'main/assert-timeout.js',
   'main/async.js',
   'main/deepEqual.js',
+  'main/diff.js',
   'main/dump.js',
   'main/each.js',
   'main/modules.js',