feat(design): add DaffSizeable to design core's public api (#2653)

libs/design/src/core/public_api.ts

@@ -14,3 +14,4 @@ export * from './article-encapsulated/public_api';
 export * from './theming/public_api';
 export * from './lazy/public_api';
 export * from './focus/public_api';
+export * from './sizeable/public_api';

libs/design/src/core/sizeable/public_api.ts

@@ -0,0 +1,11 @@
+export {
+  DaffSizeable,
+  DaffSizeAllType,
+  DaffSizeableEnum,
+  DaffSizeXSmallType,
+  DaffSizeSmallType,
+  DaffSizeMediumType,
+  DaffSizeLargeType,
+  DaffSizeXLargeType,
+} from './sizeable';
+export { daffSizeMixin } from './sizeable-mixin';

libs/design/src/core/sizeable/sizeable.ts

@@ -1,7 +1,16 @@
+/**
+ * An interface for giving a component the ability to customize sizing for component-specific UI.
+ * In order to be sizable, a component class must implement this property.
+ */
+
 export interface DaffSizeable<T extends DaffSizeAllType> {
   size: T;
 }
 
+/**
+ * The possible types that can be passed to a component that implements DaffSizeable
+ */
+
 export type DaffSizeXSmallType = 'xs';
 export type DaffSizeSmallType = 'sm';
 export type DaffSizeMediumType = 'md';