Layout Builder Browser

Enhances the layout builder block selection UX by adding:

- Custom configurable images per block.
- Custom categories for all blocks.
- Removes the extra click for "inline blocks", and merges those blocks with the
system defined blocks.
- Gives control to group blocks by categories and name each block as you want.
- Allows adding reusable block content entities dynamically.
- Allows opening the layout builder browser in a modal or in the default off-canvas.