Issue #2927349 by tim.plunkett: Decouple the Layout Builder UI from entities

core/modules/layout_builder/layout_builder.routing.yml

core/modules/layout_builder/layout_builder.services.yml

...es/layout_builder/src/Access/LayoutSectionAccessCheck.php

...es/layout_builder/src/Controller/AddSectionController.php

...s/layout_builder/src/Controller/ChooseBlockController.php

...layout_builder/src/Controller/ChooseSectionController.php

...layout_builder/src/Controller/LayoutBuilderController.php

...ules/layout_builder/src/Controller/LayoutRebuildTrait.php

...les/layout_builder/src/Controller/MoveBlockController.php

...odules/layout_builder/src/Field/LayoutSectionItemList.php

...odules/layout_builder/src/Form/ConfigureBlockFormBase.php

.../modules/layout_builder/src/Form/ConfigureSectionForm.php

.../layout_builder/src/Form/LayoutRebuildConfirmFormBase.php

core/modules/layout_builder/src/Form/RemoveBlockForm.php

core/modules/layout_builder/src/Form/RemoveSectionForm.php

core/modules/layout_builder/src/Form/UpdateBlockForm.php

.../modules/layout_builder/src/LayoutTempstoreRepository.php

...layout_builder/src/LayoutTempstoreRepositoryInterface.php

...r/src/Plugin/Derivative/LayoutBuilderLocalTaskDeriver.php

...rc/Plugin/Field/FieldFormatter/LayoutSectionFormatter.php