Add missing entity_type condition in subquery of contextual filter

It looks like in midst of porting this module to Drupal 8, the condition for checking the entity type in the subquery for the views argument handler was missed (see https://git.drupalcode.org/project/taxonomy_entity_index/-/commit/4d25cc...) even though the same condition was refactored and preserved in the views filter handler (see https://git.drupalcode.org/project/taxonomy_entity_index/-/commit/4d25cc...). Without checking the entity type, the contextual filter picks up seemingly unrelated entities.

Take the scenerio where media and content both have field_tags that use the Tags taxonomy. Also, where node:123 is tagged with your target term, and media:123 is not tagged with that term. If you have a view of all media using this term, media:123 will be included despite not being tagged with the term because 123 is an entity id in the subquery for the node (node:123) that is tagged with the term.

I could replicate it in a vanilla site with the following steps:

• In simplytest.me, enable media and this module.
• Add the tags field to the image media.
• Configure module to index both content and media.
• Created a node with nid = 1 with a tag (with tid = 2).
• Created media with mid = 1 without a tag.
• Create a view of all media.
• Add the contextual filter "Taxonomy Entity Index: Has taxonomy term ID on Media (with depth and indexed in taxonomy_entity_index)", and set the depth to 1 or more.
• View should be empty with the argument of 2, but media:1 is shown even though it has no tag.

Adding the below code to the argument handler (as in the case in /src/Plugin/views/filter/TaxonomyEntityIndexTidDepth.php:127) appears to resolve this issue:

    if (isset($this->baseTableInfo['table']['entity type'])) {
      $subquery->condition('entity_type', $this->baseTableInfo['table']['entity type']);
    }