Add link to add a new entity in an empty entity list controller table

Reroll #110 for 10.1.x

1. +++ b/core/lib/Drupal/Core/Entity/EntityListBuilder.php
   @@ -65,11 +82,17 @@ public static function createInstance(ContainerInterface $container, EntityTypeI
   +    $this->linkGenerator = $link_generator;
   

   Is the disruption of injecting the link generator worth it?

   All the other links we generate in this class (e.g. in operations) don't need/use it so that makes me feel we may not need it.

   That would dramatically reduce the complexity of this patch and the disruption to contrib.

2. +++ b/core/lib/Drupal/Core/Entity/EntityListBuilder.php
   @@ -248,4 +269,61 @@ protected function ensureDestination(Url $url) {
   +        Url::fromUri('internal:' . $this->entityType->getLinkTemplate('add-page'))
   ...
   +        Url::fromUri('internal:' . $this->entityType->getLinkTemplate('add-form'))
   

   Is internal: our only option here?

   \Drupal\Core\Entity\Controller\EntityController::addPage uses Link::createFromRoute

3. +++ b/core/lib/Drupal/Core/Entity/EntityListBuilder.php
   @@ -248,4 +269,61 @@ protected function ensureDestination(Url $url) {
   +    elseif ($this->entityType->hasLinkTemplate('add-form')) {
   

   This could return an exception if there is no add page link template, but there is an add-form link template but it requires additional parameters. So we probably would need a try/catch here.

   Also, we don't need elseif, there's a return above.

4. Coming from 🐛 Remove duplicate "add block" link from block content type view's "Results not found" message Postponed I was expecting to see something here for admin lists that are built with views, as in reality most content-entity list builders are overridden with a view. It would be good to get an issue summary update here to address what the intended course of action is there.