Create an off-canvas style library

Problem/Motivation

With the pending changes to the off-canvas reset that are happening in Drupal 10, it makes more sense than ever to re-evaluate the ecosystem surrounding the Gin admin theme and Layout Builder support.

Presently, the gin_lb → project provides fairly decent -- albeit imperfect -- off-canvas support for Drupal 9 sites, but will need to be refactored to work with Drupal 10.

Addressing this would also provide the community with a shining example of how to approach the new world of off-canvas styling for other admin themes (maybe even Claro!).

Proposed resolution

I'd like to propose that the Gin theme devise an off-canvas library following the best practices set forth in https://www.drupal.org/node/3305664 → to be included in projects like gin_toolbar and/or gin_lb. This should allow Gin to be the canonical source for all things off-canvas, which should lead to a much healthier and more stable ecosystem overall.

Remaining tasks

1. Decide what is in scope for this new library.
2. Create an off-canvas library within Gin.
3. Open a follow-up issue in gin_toolbar and optionally gin_lb that consumes the off-canvas library.

User interface changes

A brand new, shiny, and modern "off the shelf" UX for Layout Builder users.

API changes

None

Data model changes

None

What's in scope?

• Basic element types?
• Popular contrib modules?