Update CKEditor to version 4.16.0

Looking into this a bit. Is this as simple as downloading and copying over a package from https://ckeditor.com/ckeditor-4/download/?

If so, which package do I select? There are four available.

There is more to it than that. Instructions are in core/assets/vendor/ckeditor/build-config.js and you must also update core.libraries.yml with the new version.

Added Release notes snippet and tag.

Tests are green, did some (very minimal) manual testing and didn't find any problems.

Setting to Needs review to get some thorough manual testing.

This looks good, I ran the build step on my local 4.16.0 copy of ckeditor4 and got the exact same result, except for the generated timestamps of course :)

Manually tested with uploading image, selecting media, using quickedit. Everything seems normal.
I found a problem with inserting a media element using quickedit, but it's the same on 9.3.x so it's not caused by this MR. I'll look into that more to see what's causing it.

How do we decide when to update the build-config.js ? For example I noticed an editorplaceholder plugin that was newly added last year, but more recently than any changes to the plugin list in drupal core.

The plugins list in build-config.js was updated in SA-CORE-2020-001 when CKEditor was updated to 4.14, added pastefromlibreoffice
and before that in #3072382: Update CKEditor to version 4.13 when CKEditor was updated to 4.13, added pastefromgdocs

Reading about editorplaceholder, it doesn't seem like a plugin we need to add here.
It was the only update to the plugin list I saw going back to before these 2 other changes.

Sorry about the noise :/

hi,
I tested that patch #10 manually, the patch applied successfully and it works fine for me. CKEditor updated successfully.
from:
ckeditor:
version: "4.15.1"
To
ckeditor:
version: "4.16.0"
THANKYOU.

How do we decide when to update the build-config.js ? For example I noticed an editorplaceholder plugin that was newly added last year, but more recently than any changes to the plugin list in drupal core.

This only has happened a handful of times over the years since Drupal 8.0.0 shipped.

1. To add more things to the ignore key requires no discussion: this is just to automatically ignore whatever additional metadata files the CKSource team committed to the repository, that we do not need to ship with Drupal.
2. To add more things to the plugins key does require scrutiny, since this fundamentally changes our CKEditor build. The last time this happened was in November 2019, for updating to CKEditor 4.13, in #3072382: Update CKEditor to version 4.13. That included a new pastefromgdocs plugin that made sense to add in addition to the pre-existing pastefromword plugin. Before then it was #2239419: Include CKEditor's AutoGrow plug-in that added the autogrow plugin. This required detailed discussion.
   EDIT: I should've read #12 before writing all this 🙃

So, let's look at what's changing here … nothing — great! 👍

For example I noticed an editorplaceholder plugin that was newly added last year, but more recently than any changes to the plugin list in drupal core.

Adding that would require a separate issue, because it changes the UX materially.

Reading about editorplaceholder, it doesn't seem like a plugin we need to add here.

Agreed!

Given

This looks good, I ran the build step on my local 4.16.0 copy of ckeditor4 and got the exact same result, except for the generated timestamps of course :)

and

Manually tested with uploading image, selecting media, using quickedit. Everything seems normal.

I don't see any reason to not go ahead with committing this 😊

Committed/pushed to 9.3.x and cherry-picked to 9.2.x, thanks!