[D7] Convert drupalSettings from JavaScript to JSON, to allow for CSP in the future

Updated the patch from #33 to apply cleanly to the latest version.

The patch on #45 looks good to me, and has been working fine on some production sites for a while.

We looked at getting this one into 7.103 but didn't manage to do so.

I think this only makes sense if it makes absolutely no changes on a D7 site that does not enable the option.

The complete lack of JS testing in D7 makes it particularly risky to introduce something like this.

For example @poker10 spotted this straight away:

        'misc/drupal.js' => array(
          'data' => 'misc/drupal.js',
          'type' => 'file',
          'scope' => 'header',
          'group' => JS_LIBRARY,
          'every_page' => TRUE,
-         'weight' => -1,
+        'weight' => -2,
          'requires_jquery' => TRUE,

That would affect all sites whether they implemented the new option or not.

Perhaps that's no big deal, but with no automated testing it's hard to tell.. plus who knows what the consequences would be for real sites with lots of modules installed. Some may have carefully tweaked all of the relative weights.. possibly years ago.

My acceptance criteria for this would be that if the new option is not enabled, absolutely nothing changes.

Converted drupal-2783153-45.patch to an MR.

It does seem to cause one test to fail (not verified causation but seems like a strange coincidence if not):

JavaScript 160 passes, 1 fail, 1 exception, and 10 debug messages

---------------------
---- JavaScriptTestCase ----
Status    Group      Filename          Line Function                            
--------------------------------------------------------------------------------
Exception Warning    locale.inc        1527 _locale_parse_js_file()            
    file_get_contents(misc/drupal-settings-loader.js): Failed to open stream: No
    such file or directory
Fail      Other      common.test       1693 JavaScriptTestCase->testJavaScriptA
    When "javascript_always_use_jquery" is FALSE: The front page of the site
    does not include Drupal settings loader.