Update CKEditor library to 4.6

#2 doesn't yet bring in the new Moono-Lisa skin. Perhaps that's better to leave for a follow-up.

We'll still need guidance from the CKEditor team regarding point 4: config.image2_altRequired.

Drupal 8's CKEditor integration doesn't currently support "random file uploads". It only supports images. https://www.drupal.org/project/editor_file adds support for files. Ideally, that module would be refactored to support the Upload File plugin (which is btw for drag-and-drop file uploads). And then that module could be proposed for core inclusion.

For drag-and-drop image uploads, see #2560457: Support drag-and-drop image uploads in CKEditor.

In fact, filed a feature request for that: #2828842: Consider supporting drag-and-drop file uploads in CKEditor, by supporting CKEditor core's "uploadfile" plugin.

Great :)

Opened a follow-up to evaluate switching to the new Moono-Lisa skin: #2831442: Switch to CKEditor 4.6's new "Moono-Lisa" skin.

#10 + #11: thanks! However, #10 confirmed my suspicion, which is why #11 is irrelevant: we don't rely on image2's dialogs, hence also not its translations. I was mainly asking this to ensure that there are no internal expectations around this. We do use all of the logic/internals of image2, we just don't use its default UI.

Also, landing this will fix #2827994: [upstream] Bug with clearing the text when pasting from the Word. Which means we should consider (for the first time) also adding this to Drupal 8.2.x.

Alright, let's get this going again.

Now we're already at 4.6.2: http://ckeditor.com/blog/CKEditor-4.6.2-released.

• 4.6.1 only brought bugfixes: http://ckeditor.com/blog/CKEditor-4.6.1-released
• 4.6.2 also adds a new localization: Azerbaijani. I'll need to make sure that Drupal's langcode matches CKEditor's, or ensure the necessary mapping metadata is set

Will work on this on Monday probably.

Also, @tkoleary has volunteered to take on anything that's necessary to get us to switch to Moono-Lisa: #2831442-5: Switch to CKEditor 4.6's new "Moono-Lisa" skin

NW per #15.

Agreed on the skin!

I don't see the value in updating to 4.6.0 instead of 4.6.2 though: same amount of work. More review work, and more committer work.

Per #21.

Working on the manual testing now.

Typo.

Manual testing completed. Remarks:

1. I really love the improved keyboard shortcuts visibility (it's what I asked for years ago!)
2. Our captioned image widget still behaves exactly the same.
3. #2827994: [upstream] Bug with clearing the text when pasting from the Word already proved this indeed greatly enhances pasting from Word, just as http://ckeditor.com/blog/CKEditor-4.6-released promises

Technical remarks:

1. From the IS:
   

   4. … other improvements, including one worth calling out here: a config.image2_altRequired setting to require the ALT attribute on images. But Drupal 8 always required that already anyway, so it doesn't affect us. Except that since the drupalimage plugin extends the image2 plugin, it's possible that we may need to make some small adjustments.

   I tested this extensively, but this has no effect on us. We're already requiring alt text, and are allowing only explicit opt out. The explicit opt out also still works. As http://docs.ckeditor.com/#!/guide/dev_captionedimage-section-making-alte... shows, this is only relevant for the default UI of the CKEditor image2 plugin, which we don't use at all.

2. I didn't notice this in my original analysis, so it wasn't in the IS. But in my (thorough) testing, I noticed that CKEditor 4.6 added the Occitanlocalization. Its langcode is oc. This matches Drupal's langcode. See https://localize.drupal.org/translate/languages/oc. This means no additional work is necessary (i.e. no additional language mapping needs to be added to core/modules/language/config/install/language.mappings.yml (like we did in #2050097: Map CKEditor languages to Drupal languages).

Therefore, this patch is actually already good to go! :)

Yay, and also thanks for creating that follow-up already!