Create patterns/components for grid management

I realized that in Layout Builder, the drag&drop feature which allows to move blocks to other regions or sections is not working with layouts generated from patterns.

Also for patterns used as layouts, UI Styles Layout Builder is not able to add classes to a layout region because otherwise we would need to use the region_attributes variable generated by
https://git.drupalcode.org/project/drupal/-/blob/11.x/core/modules/layou...

I think this needs a discussion.

I opened a WIP MR with col 1 and col 4 for discussion.

Third problem. Configuration form UI, see screenshot.

Discussed with @pdureau,

The mechanism depends on region_attributes, created by template_preprocess_layout in layout_discovery module.

However, this region_attributes variable is not used in component templates. (and it does not exist if the component is not used as a layout.)

The solution would be to enforce every UI patterns component to use one attributes object by slot. But it will not possible when slots are printed without wrappers.

<div{{ attributes }}>
  <div{{ foo_attributes.addClass('foo')}}>
    {{ foo }}
  </div>
  {{ bar }}
 </div>

Also, it would not be possible to use the prop drilling from UI Styles because we do not have access to the content of the slots to inject the wrapper. (it is removed when rendering and blocks are rendered twice)