Create an interface to share the definition of the overridable methods on DefaultsSectionStorageInterface and LayoutEntityDisplayInterface

Problem/Motivation

\Drupal\layout_builder\Entity\LayoutEntityDisplayInterface::isOverridable()
\Drupal\layout_builder\Entity\LayoutEntityDisplayInterface::setOverridable()
\Drupal\layout_builder\DefaultsSectionStorageInterface::isOverridable()
\Drupal\layout_builder\DefaultsSectionStorageInterface::setOverridable()

Proposed resolution

Make a shared OverridableInterface

Remaining tasks

User interface changes

API changes

Data model changes