Add support for Views blocks and code defined blocks

I don't think it makes sense to start special casing various type of blocks and adding individual support for each. Can we find some generic way to allow all-kind of blocks to opt-into rendering correctly?

in particular since we have two place rendering blocks - layout-builder and blocks-layout integration, we have to resolve it without code-duplication.

this is how blocks are handled generically for layout-builder:
https://git.drupalcode.org/project/custom_elements/-/blob/8.x-2.x/src/Pr...

Could we simply do the same here and have both content-entity and views block working?

Still, I think we need to introduce a way to add custom code per-block class that builds the block into custom-elements. So far, we've been doing that by swapping out the block-class for our projects:

/**
 * Implements hook_block_alter().
 *
 * Alter the block plugin definitions for Layout builder's inline blocks.
 */
function ldp_layout_builder_block_alter(&$definitions) {
  foreach ($definitions as $id => $definition) {
    if (strpos($id, 'inline_block:') === 0) {
      $definitions[$id]['class'] = LdpInlineBlock::class;
    }
    if (strpos($id, 'block_content:') === 0) {
      $definitions[$id]['class'] = LdpContentBlock::class;
    }
  }
}

and then this build method:

   * {@inheritdoc}
   */
  public function build() {
    if ($this->getCurrentRequest()->getRequestFormat() == 'custom_elements') {
      $block = $this->getEntity();
      $custom_element = $this->getCustomElementGenerator()
        ->generate($block, $this->configuration['view_mode']);
      return $custom_element->toRenderArray();
    }
    return parent::build();
  }

let's discuss how to do that best!