Issue #2446869 by amateescu: Convert the "Field storage edit" form to an actual entity form

core/lib/Drupal/Core/Field/FieldItemInterface.php

core/modules/comment/comment.module

core/modules/comment/src/Tests/CommentFieldsTest.php

core/modules/comment/src/Tests/CommentNonNodeTest.php

...s/entity_reference/src/Tests/EntityReferenceAdminTest.php

core/modules/field_ui/field_ui.module

.../modules/field_ui/src/Form/FieldStorageConfigEditForm.php

core/modules/field_ui/src/Routing/RouteSubscriber.php

core/modules/field_ui/src/Tests/ManageFieldsTest.php

core/modules/file/src/Plugin/Field/FieldType/FileItem.php

core/modules/file/src/Tests/FileFieldWidgetTest.php

core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php

core/modules/image/src/Tests/ImageFieldDisplayTest.php

core/modules/options/src/Tests/OptionsFieldUITest.php

...modules/options/src/Tests/OptionsFloatFieldImportTest.php