refactor(@schematics/angular): rename guard param of generated file

Closes #18601

Author: Ayudh

packages/schematics/angular/guard/files/__name@dasherize__.guard.ts.template

@@ -7,12 +7,12 @@ import { Observable } from 'rxjs';
 })
 export class <%= classify(name) %>Guard implements <%= implementations %> {
   <% if (implements.includes('CanActivate')) { %>canActivate(
-    next: ActivatedRouteSnapshot,
+    route: ActivatedRouteSnapshot,
     state: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
     return true;
   }
   <% } %><% if (implements.includes('CanActivateChild')) { %>canActivateChild(
-    next: ActivatedRouteSnapshot,
+    childRoute: ActivatedRouteSnapshot,
     state: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
     return true;
   }