Views preview query output type error

Problem/Motivation

When creating a View the preview crashes if the query display is enabled.

Steps to reproduce

Install External Entities and External Entities Views Integration.
Configure an external entity.
Enable the query display in Views.
Build a view of the external entity.

The preview cannot be rendered because Views UI assumes the query can be implicitly cast to a string in core/modules/views_ui/src/ViewUI.php:

$query_string = $executable->build_info['query'];
 ...
'#context' => ['query' => strtr($query_string, $quoted)],

Proposed resolution

Make EE's Query object implement \Stringable and add a dummy __toString method.

Remaining tasks

None

User interface changes

None (The preview works, though the querystring is just a placeholder.)

API changes

None

Data model changes

None