[DOC release] include QP-only transitionTo info

Both `Route.transitionTo` and `RouterService.transitionTo` support
query-params-only transitions, where the caller invokes the method
like `transitionTo({ queryParams: { ... } })`.

(cherry picked from commit f63c27e)

packages/@ember/-internals/routing/lib/services/router.ts

@@ -110,11 +110,12 @@ export default class RouterService extends Service {
      ```
 
      @method transitionTo
-     @param {String} routeNameOrUrl the name of the route or a URL
-     @param {...Object} models the model(s) or identifier(s) to be used while
+     @param {String} [routeNameOrUrl] the name of the route or a URL
+     @param {...Object} [models] the model(s) or identifier(s) to be used while
        transitioning to the route.
      @param {Object} [options] optional hash with a queryParams property
-       containing a mapping of query parameters
+       containing a mapping of query parameters. May be supplied as the only
+      parameter to trigger a query-parameter-only transition.
      @return {Transition} the transition object associated with this
        attempted transition
      @public

packages/@ember/-internals/routing/lib/system/route.ts

@@ -785,11 +785,12 @@ class Route extends EmberObject implements IRoute {
     ```
 
     @method transitionTo
-    @param {String} name the name of the route or a URL
-    @param {...Object} models the model(s) or identifier(s) to be used while
+    @param {String} [name] the name of the route or a URL.
+    @param {...Object} [models] the model(s) or identifier(s) to be used while
       transitioning to the route.
     @param {Object} [options] optional hash with a queryParams property
-      containing a mapping of query parameters
+      containing a mapping of query parameters. May be supplied as the only
+      parameter to trigger a query-parameter-only transition.
     @return {Transition} the transition object associated with this
       attempted transition
     @since 1.0.0