Some path alias crash the creation of the views_url_alias table

Problem/Motivation

Path aliases pointing to something else than a ContentEntityInterface generate

```
TypeError: views_url_alias_get_path_entity_type(): Return value must be of type ?Drupal\Core\Entity\ContentEntityInterface, [SOMETHING ELSE] returned
```
Example: Drupal\webform\Entity\Webform

Steps to reproduce

Add a Webform with an alias and install the module

Proposed resolution

Change the return type to EntityInterface

API changes

```
function views_url_alias_get_path_entity_type will return null or EntityInterface instead of null or ContentEntityInterface
```