Issue #2313823 by tim.plunkett, martin107: Use FormStateInterface for all typehints.

core/includes/ajax.inc

core/includes/form.inc

core/modules/book/book.module

core/modules/comment/comment.module

core/modules/content_translation/content_translation.module

...les/content_translation/src/ContentTranslationHandler.php

...nt_translation/src/ContentTranslationHandlerInterface.php

core/modules/dblog/dblog.module

core/modules/editor/editor.module

core/modules/entity/src/Entity/EntityFormDisplay.php

core/modules/entity_reference/entity_reference.module

...ules/field_third_party_test/field_third_party_test.module

core/modules/field_ui/field_ui.api.php

core/modules/field_ui/field_ui.module

.../modules/file/src/Plugin/Field/FieldWidget/FileWidget.php

core/modules/locale/locale.module

core/modules/menu_ui/menu_ui.module

core/modules/node/src/Plugin/Search/NodeSearch.php

core/modules/path/path.module

core/modules/search/src/Plugin/SearchInterface.php