feat(type declarations): Refine the type

signature of the activationStrategy enumeration with additional
information

Added the ActivationStrategy interface to describe the shape of the
activationStrategy object that enumerates router activation strategies.

src/interfaces.js

@@ -170,3 +170,21 @@ interface ConfiguresRouter {
   */
   configureRouter(config: RouterConfiguration, router: Router): Promise<void>|PromiseLike<void>|void;
 }
+
+/**
+* An optional interface describing the available activation strategies.
+*/
+interface ActivationStrategy {
+  /**
+  * Reuse the existing the view model without invoking lifecycle hooks.
+  */
+  noChange: 'no-change';
+  /**
+  * Reuse the existing the view model, invoke Router lifecycle hooks.
+  */
+  invokeLifecycle: 'invoke-lifecycle';
+  /**
+  * Replace the existing view model, invoking Router lifecycle hooks.
+  */
+  replace: 'replace';
+}

src/navigation-plan.js

@@ -4,7 +4,7 @@ import {_resolveUrl} from './util';
 /**
 * The strategy to use when activating modules during navigation.
 */
-export const activationStrategy = {
+export const activationStrategy: ActivationStrategy = {
   noChange: 'no-change',
   invokeLifecycle: 'invoke-lifecycle',
   replace: 'replace'