Add a primary key to the {taxonomy_index} table and prevent duplicates being inserted

[webnicola]

Problema chiave primaria tabella tassonomia

https://www.drupal.org/project/drupal/issues/610076

Problems with {taxonomy_index} table:
No primary key.
No vid column thus cannot index on that missing field.
No language column thus cannot differentiate between usages in different languages.

Patch: https://www.drupal.org/files/issues/2021-03-05/drupal-n610076-88.patch