Update CKEditor plugin to be compatible with Drupal 8.8

Here's the fix. It updates the plugin to use new drupallink API with a fallback for backwards compatibility.

Handling case where drupallink doesn't exist:

-      if (CKEDITOR.plugins.drupallink.hasOwnProperty('registerLinkableWidget') === false) {
+      if (typeof CKEDITOR.plugins.drupallink === 'undefined' || CKEDITOR.plugins.drupallink.hasOwnProperty('registerLinkableWidget') === false) {

I can't recreate the failure in the 8.8 test in comment #6 locally. I'm trying to adjust the code to be more robust, let's see if this helps.

Reverting the change to the test in #8 as it didn't help. I'm now kind of stuck on this. I can't reproduce the failure locally, and I'm not sure why it's failing.

. I'm now kind of stuck on this. I can't reproduce locally.

Testing another set of changes on testbot.

Alright, sweet! Now I can see the bug locally, I needed to update composer in the root of the repo:

> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Updating behat/mink dev-master (9ea1ceb => a534fe7):     The package has modified files:
    M src/Element/TraversableElement.php
    M tests/Element/DocumentElementTest.php
    Discard changes [y,n,v,d,s,?]? y
 Checking out a534fe7dac
> Drupal\Core\Composer\Composer::vendorTestCodeCleanup
  - Updating behat/mink-selenium2-driver dev-master (93474c6 => 8684ee4):  Checking out 8684ee4e63
> Drupal\Core\Composer\Composer::vendorTestCodeCleanup

I think I have it now. I was able to reproduce and fix the autocomplete bug locally on 8.8.

The issue is some change in either behat or the selenium driver that was causing the focus to change after filling in the field, making the autocomplete disappear.

I borrowed a fix from EntityReferenceAutocompleteWidgetTest:

$autocomplete_field->setValue('Test');
$this->getSession()->getDriver()->keyDown($autocomplete_field->getXpath(), ' ');

Oops, attached the patch twice instead of the interdiff in the last comment.

This $this->assertSession()->waitOnAutocomplete(); is perhaps unnecessary. It was working without it, but EntityReferenceAutocompleteWidgetTest has it, and it seems like it might make the test more stable, so throwing it in.

Phenaproxima raised the issue that checking if the drupallink plugin exists before adding the workaround doesn't make sense:

The only real red flag, for me, is typeof drupallink === 'undefined'

If drupallink is undefined, why would we want to put the BC layer there?

Testing changing the logic so that workaround isn't added if drupallink not enabled. This makes more sense. I was fixing the bug where CKEDITOR.plugins.drupallink.hasOwnProperty('registerLinkableWidget') was throwing an error by adding a check if

typeof CKEDITOR.plugins.drupallink === 'undefined'

But linking shouldn't be enabled without CKEDITOR.plugins.drupallink, so reversing the logic:

typeof CKEDITOR.plugins.drupallink !== 'undefined'

Triggered a retest for #18 after #2994699: Create a CKEditor plugin to select and embed a media item from the Media Library went in to 8.8. And it passed: all green!

Re #20.2:
After looking at registerLinkableWidget(), I see it takes a string, so we can do it before the plugin is instantiated, so moving the code into beforeInit() method of drupalentity plugin, right where the other condition sits.

Re #20.3:
The change to ContentTranslationTest has to do with #13. Some change to Behat or Selenium was breaking my autocomplete test code. Fixed in #14. I don't know the cause of it, but I was able to adjust the code, by borrowing the process used to test entity reference autocomplete fields.

@@ -124,10 +128,8 @@ class ContentTranslationTest extends EntityEmbedTestBase {
     $this->drupalLogin($this->translator);
     $this->drupalGet('node/' . $host->id() . '/edit');
     $this->waitForEditor();
-    $this->assertSession()
-      ->waitForElementVisible('css', 'a.cke_button__test_node')
-      ->click();
-    $this->assertSession()->waitForId('drupal-modal');
+    $this->pressEditorButton('test_node');
+    $this->assertTrue($this->assertSession()->waitForElementVisible('css', '#entity-embed-dialog-form'));

Wrapping the whole thing in if (editor.plugins.drupallink).

I forgot, this was the same reason I had failures in #3 (fixed in #6). In some cases editor.plugins.drupallink is undefined.

This passed all the function javascript tests for me locally on Drupal 8.8.

I think this is in a good place now. Ready for another review.

I think the linter was complaining the comment didn't start with a capital letter. I'll just revert the change on commit.

Committed!