Add view tab + standard template for block content

Problem/Motivation

https://www.drupal.org/project/block_content_template something like this

Steps to reproduce

NA

Proposed resolution

Add a view tab to the block content entity
Add default template when using the view route of the block only As a preview of what the block will look like if that helps

Remaining tasks

Review if it's worth it
Implement
Write test
code review

User interface changes

New tab to "View" block without being placed on a page

New view tab

View page

API changes

NA

Data model changes

NA

Release notes snippet

TBD