Adopt layout library to allow for providing multiple templates per content type

[pyrello]

Motivation

Layout Library - https://www.drupal.org/project/layout_library - is a module that allows for multiple layout templates to be created per content type. A user can then select that layout as the starting point for the page instead of the default layout template. Currently, the way that the module works is counterintuitive - it only allows for selecting a layout template, but not for overriding it. A solution to this is being discussed here: https://www.drupal.org/project/layout_library/issues/3082434 and a proposed patch exists. However, this patch depends on functionality that has been committed to Drupal 9.1.x and the backported patch is not currently working.

Proposed solution

• Add Layout Library as a dependency and turn it on by default
• If we want to pursue this prior to our being able to transition to 9.1.x, we will need to fix the existing patch that is posted at this comment: https://www.drupal.org/project/drupal/issues/3143635#comment-13706626. The problem with the current patch is that when it applies, it creates a broken PHP class file that causes the site to error out. A new patch could be posted at that issue queue to allow us to grab it from there.
• Add the patch for layout library from this comment: https://www.drupal.org/project/layout_library/issues/3082434#comment-13725884. This patch may need some additional tweaking. I have not been able to test it yet.
• Create an alternate layout that can be used for a page.
• Possibly create a way for the user to change the layout in a different place than on the edit page, which seems counterintuitive.
• Possibly create a way to display an icon for the layout templates to allow the user to select something based on visual clues.

[mjoneill]

Dentistry is planning a redesign and asked about this functionality. Tight deadline, multiple participants who will be creating pages, etc... the lead wants to know how to help avoid blank page syndrome...

@ABoston88

[pyrello]

I started working on a proof of concept/demo PR for the Layout Library. I could get something pushed to dev before too long to see how we might use that.

[mjoneill]

I started working on a proof of concept/demo PR for the Layout Library. I could get something pushed to dev before too long to see how we might use that.

Sure. We did not commit to moving this up in the prioritization queue. Just making it visible...

[pyrello]

Encouraged by @bspeare, I pushed up the work I did on this earlier in the year: #4155