docs(router): migrate deprecated @whatItDoes tags (#23187)

The first line of the description is now used as an overview.

PR Close #23187

packages/router/src/directives/router_link.ts

@@ -18,11 +18,9 @@ import {UrlTree} from '../url_tree';
 
 
 /**
- * @whatItDoes Lets you link to specific parts of your app.
- *
  * @description
  *
- * The RouterLink directives let you link to specific parts of your app.
+ * Lets you link to specific routes in your app.
  *
  * Consider the following route configuration:
  * `[{ path: 'user/:name', component: UserCmp }]`.
@@ -154,7 +152,9 @@ export class RouterLink {
 }
 
 /**
- * @whatItDoes Lets you link to specific parts of your app.
+ * @description
+ *
+ * Lets you link to specific routes in your app.
  *
  * See {@link RouterLink} for more information.
  *

packages/router/src/directives/router_link_active.ts

@@ -16,11 +16,12 @@ import {RouterLink, RouterLinkWithHref} from './router_link';
 
 
 /**
- * @whatItDoes Lets you add a CSS class to an element when the link's route becomes active.
  *
  * @description
  *
- * The RouterLinkActive directive lets you add a CSS class to an element when the link's route
+ * Lets you add a CSS class to an element when the link's route becomes active.
+ *
+ * This directive lets you add a CSS class to an element when the link's route
  * becomes active.
  *
  * Consider the following example:

packages/router/src/directives/router_outlet.ts

@@ -13,11 +13,10 @@ import {ActivatedRoute} from '../router_state';
 import {PRIMARY_OUTLET} from '../shared';
 
 /**
- * @whatItDoes Acts as a placeholder that Angular dynamically fills based on the current router
- * state.
- *
  * @description
  *
+ * Acts as a placeholder that Angular dynamically fills based on the current router state.
+ *
  * ```
  * <router-outlet></router-outlet>
  * <router-outlet name='left'></router-outlet>