#3520438 Layers now using dndkit!

Closes #3520438

Layers refactored and much improved to use DNDkit.

1. Dragon 🐉 Drop is now much smoother in the layers panel. It should be eas(y||ier) to place the items exactly where you like. Moving left to right allows finer control of the nested level when at the bottom of a slot. Flickering when hovering on/near the edge of a valid drop location should be greatly reduced if not eliminated entirely.
2. Should be able to scroll while dragging - either with the mouse wheel or by moving to the top/bottom of the tree component. (Fixes https://www.drupal.org/project/experience_builder/issues/3498598 and https://www.drupal.org/project/experience_builder/issues/3470603)
3. Should not be possible to drag a parent into its child(ren)! When dragging a parent, it and all its descendants will be greyed out and disabled as valid drop targets.
4. Fixed a bug where when dragging (either preview or layers) and scrolling the drag operation would be interrupted.
5. Fixed [https://www.drupal.org/project/experience_builder/issues/3515836\\] - the drag overlay should now correctly be positioned just to the bottom right of the mouse cursor even if you drag fast.
6. Updated a few styles to make things look a bit cleaner.

global-regions.cy.js is failing on head so I don't think that blocks this from being merged.