Ability to display block_content entities independently, also outside of Blocks

Problem/Motivation

When I display a custom block using the block layout configuration the block prints using the block.html.twig template however if I have a custom block view each row is just the rendered fields, not the whole rendered block.
This causes problems for themers and is inconsistent with similar row formats like "Show: Content" for nodes.

This also means that contextual links don't show for blocks in a view.

Steps to reproduce:

1. Create a custom block
2. Create a view showing custom blocks
3. For the view format select Show = Custom block

Proposed resolution

For this "Show: Content block" row type the row should be the rendered block, not just the fields.
If you want individual fields you would choose "Show: Fields" instead.