chore: use "export *" for overlay-config (#7218)

Author: jelbourn

src/cdk/overlay/public_api.ts

@@ -36,11 +36,11 @@ export const OVERLAY_PROVIDERS: Provider[] = [
 export class OverlayModule {}
 
 
+export * from './overlay-config';
 export {Overlay} from './overlay';
 export {OverlayContainer} from './overlay-container';
 export {FullscreenOverlayContainer} from './fullscreen-overlay-container';
 export {OverlayRef} from './overlay-ref';
-export {OverlayConfig} from './overlay-config';
 export {ConnectedOverlayDirective, OverlayOrigin} from './overlay-directives';
 export {ViewportRuler} from '@angular/cdk/scrolling';
 export {ComponentType} from '@angular/cdk/portal';