Runtime debug statement in Views now prints out object

Problem/Motivation

\Drupal\views\ViewExecutable::setDisplay() includes a helpful debug() statement if you try to set an invalid display.
However, this can be shown to end-users if a site is misconfigured.

What's more, when format_string() was converted to result in an object, the debug statement now shows it as an object!

Debug:
Drupal\Component\Render\FormattableMarkup Object
(
    [arguments:protected] => Array
        (
            [@display] => block_1
        )

    [string] => setDisplay() called with invalid display ID "@display".
)
in Drupal\views\ViewExecutable->setDisplay() (line 792 of core/modules/views/src/ViewExecutable.php).

Proposed resolution

Either fix the debug statement, or remove it.

Remaining tasks

Credit http://drupal.org/u/tinny (who was the one who found this)

User interface changes

API changes

Data model changes