Layout Builder Browser Library

I pushed a first draft.

Here is what it looks like:

I will try to do the "in Layout Builder when hovering a block, display this more detailed image" or maybe replace it with a link.

Also maybe there are some update path to do to init values.

About "in Layout Builder when hovering a block, display this more detailed image", as the block link in Layout Builder Browser already wraps the image, it is no possible to make the image a link that points to the library image.

Also an on hover behavior, I guess would mean needing an external JS library and I don't want to introduce dependencies.

So putting the status in "Needs review" and waiting for maintainers feedback.

Attaching patch from MR for easier Composer usage.

Converting unordered list into unstyled list.