LayoutEntityHelperTrait::isLayoutCompatibleEntity() should check whether the entity type has a view builder class

Problem/Motivation

\Drupal\layout_builder\LayoutEntityHelperTrait::isLayoutCompatibleEntity() is invoked on every entity presave by \Drupal\layout_builder\InlineBlockEntityOperations::handlePreSave(), and the code for checking layout_builder compatibility is quite expensive and involves creating contexts and whatnot.

Proposed resolution

Entity types that don't have a view builder handler (most config entities) can never be managed by Layout Builder, so we should add check for that.

Remaining tasks

Review.

User interface changes

Nope.

API changes

Nope.

Data model changes

Nope.

Release notes snippet

Nope.