Replacing(?) jQuery UI resizable

I think there may be a legitimate need for horizontally resizable off-canvas dialogs. Even anecdotally, I've seen Layout Builder users increase the width of off-canvas dialogs with long forms or CKEditor. For this reason, I think off-canvas dialogs should remain resizable. If even bnjmnm the hermit has seen this in the outside world, there are probably enough users enjoying the feature that it needs still be available.

To keep this specific functionality without the overhead of shimming+replicating yet another massive jQuery UI widget I propose:
- Add a feature specific to off-canvas dialogs that provides only horizontal resizability.
- Any calls to resizable() that only result in horizontal off-canvas reziability will be cancelled in favor of the the new off-canvas-specific feature.
- Calls to resizable() that expect something more that horizontal off-canvas resizability will trigger a deprecation warning.

This approach would provide a regression-free experience for all core dialog uses, and provide deprecation warnings for any (I think unlikely) scenarios of resizable dialogs being used beyond that in contrib/custom.

Something that suggests many users are not aware that off-canvas dialogs are resizable: the Layout Builder Modal module. It's possible I'm misunderstanding this part of the module summary, bit it sounds like it was created primarily to provide more width to layout builder dialogs?

The interface for the user to write content within this custom block would be through the off-canvas dialog which is the standard solution selected by the Layout Builder developers. The off-canvas dialog is very narrow and not an optimal user experience for this scenario, so to provide the author with a better interface this module let’s you use a modal dialog instead.

Re #10

So how do we know where it is used in core?

Fortunately this is fairly easy to narrow down. jQuery UI dialog is not accessed directly, but via drupal.dialog: library. This library includes
misc/dialog/dialog.position.js: {} which changes the dialog default settings to disabling resizable by default:

// autoResize option will turn off resizable and draggable.
  drupalSettings.dialog = $.extend(
    { autoResize: true, maxHeight: '95%' },
    drupalSettings.dialog,
  );

Since this is the default, it's only necessary to find places where the defaultautoResize true is changed to false. This happens in two places:

1. Off-canvas. The setting is overridden in off-canvas dialogs inside
   \Drupal\Core\Ajax\OpenOffCanvasDialogCommand::__construct, which includes
   $this->dialogOptions['autoResize'] = FALSE;
2. Dialogs used by CKEditor when the viewport is under 600px. see core/modules/ckeditor/js/ckeditor.es6.js which includes
   

   dialogSettings.autoResize =
           window.matchMedia('(min-width: 600px)').matches;

So dialogs triggered by CKEditor are resizable at these narrower viewport widths. Some things worth noting:

• CKEditor 5 will use dialogs provided by the CKEditor 5 library, no Drupal dialogs used
• When used with Seven, it resizes the content area, but not the title bar or button pane. I could not find an issue for this, which does not surprise me. At these narrower widths, a user is most likely on a touch device and would not think to drag to resize a dialog, nor do I think they'd have a need to make it smaller
  
• In Claro, resizing a (not off-canvas) dialog makes it flat-out vanish at any viewport width. So resizing definitely doesn't work for those core CKEditor uses right now. though it's There is an issue for this: #3186463: Dialog resize issue, and all of the examples are with non-core uses such as the token browser.
  
• Dialog resizing works for these CKEditor dialogs in Stark/Stable, so it's possible there are users enjoying this feature on themes that aren't Seven or Claro. It doesn't look that great of a user experience as the form elements don't resize, and I still think it's unlikely that a mobile user would try to reduce the width of a dialog, but theoretically there could be users that use this feature.
  

I grepped through contrib to find places where autoResize was set to something other than the default TRUE, which disables resize: http://grep.xnddx.ru/search?text=autoresize&filename=

Just a quick review of those results provides a sense of what is likely needed:

• Paragraphs and Entity Browser disables autoResize but explicitly disable resize, so these don't need resizability
• Token disables autoResize, which is expected as it was mentioned earlier that token uses resizable (and draggable) dialogs
• The Paragraphs Previewer module appears to be used by a nontrivial amount of sites, and this has resizable dialogs.

Aside from the evidence that at least two popular modules use dialog for resizability, it also shows that there is contrib expectation for dialog draggability. These two features are heavily integrated with the drupal.dialog API and its custom events. They're not easily swapped out with contrib-provided versions of jQuery UI resizable/draggable. It may be necessary to provide a legacy version of drupal.dialog that continues to use jQuery UI assets, and can be used simultaneously with whatever dialog solution is added that doesn't use jQuery UI.

Updated proposal based on the prior two comments:

1. #14 confirmed that core only uses resizable dialogs in Off Canvas and CKEditor 4 dialogs when the width is under 600px
2. #15 established that it's not uncommon for contrib to enable resize on dialogs. It was also clear that other not-used-by-core jQuery UI dialog features such as draggable are used, and they're used via Drupal.dialog, not direct interaction with jQuery UI. If core loses draggability/resizability on dialogs, contrib modules requiring these features wouldn't be able to get them by simply adding the contrib modules for jQuery UI resizable, draggable, etc

Proposed solution for core

• The jquery.ui.resizable is already deprecated
• Off Canvas dialogs will stop using resizable and we will add custom resizability (unless a good library has become available since my last search... not too many options unless we use Vue/React).
• The other core use of resizable - CKEditor dialogs in <600px viewports - will be left as-is as the entire module will soon be deprecated

Proposed solution for contrib/custom

• A jq_dialog module that provides the jQuery-UI-using Drupal.dialog. That can be used simultaneously with Drupal core's eventual non-Jquery-UI-dialog. Modules should be able to add jq_dialog as a dependency, then find/replace uses of Drupal.dialog() with Drupal.jqDialog(), and dialogs will continue to work as expected.
• Ideally, I'd like to provide console warnings before #2158943: PP-1 Add a native dialog element using HTMX to deprecate the jQuery UI dialog lands. The warnings would triggered for any Drupal.dialog feature that will no longer be available with the jQuery UI dialog replacement, and refer projects to jq_dialog as a way to continue use of this functionality. I.e. a console warning would be triggered for any dialogs with resizable or draggable set to TRUE. This would give projects sufficent time to add jq_dialog as a dependency, instead of being surprised by a dialog replacement that doesn't support dragging or resize.