Template suggestions for custom block view modes

Problem/Motivation

Unlike nodes, block entities do not have theme suggestions for view modes on custom block types. This means that if you need to create a template for a block in a specific display mode, then you need to write custom code to pick it up.

Steps to reproduce

NA

Proposed resolution

<!-- FILE NAME SUGGESTIONS:
   * block--content--id--olivero-myfirstblock.html.twig
   * block--content.html.twig
   * block--olivero-myfirstblock.html.twig
   * block--block-content--ec97a186-c1e4-41d7-8527-6bb0e0045e47.html.twig
   * block--block-content--id-view--olivero-myfirstblock--full.html.twig
   * block--block-content--id--olivero-myfirstblock.html.twig
   * block--block-content--view-type--basic--full.html.twig
   * block--block-content--type--basic.html.twig
   * block--block-content--view--full.html.twig
   * block--block-content.html.twig
   x block.html.twig

Remaining tasks

Framework manager review
Review

User interface changes

NA

API changes

NA

Data model changes

NA

Release notes snippet

NA