fix(router): Update Navigation#initialUrl to match documentation an…

…d reality (angular#43863)

BREAKING CHANGE:

* The type of `initialUrl` is set to `string|UrlTree` but in reality,
  the `Router` only sets it to a value that will always be `UrlTree`
* `initialUrl` is documented as "The target URL passed into the
  `Router#navigateByUrl()` call before navigation" but the value
  actually gets set to something completely different. It's set to the
  current internal `UrlTree` of the Router at the time navigation
  occurs.

With this change, there is no exact replacement for the old value of
`initialUrl` because it was enver intended to be exposed.
`Router.url` is likely the best replacement for this.
In more specific use-cases, tracking the `finalUrl` between successful
navigations can also be used as a replacement.

PR Close angular#43863

goldens/public-api/router/index.md

@@ -268,7 +268,7 @@ export interface Navigation {
     extras: NavigationExtras;
     finalUrl?: UrlTree;
     id: number;
-    initialUrl: string | UrlTree;
+    initialUrl: UrlTree;
     previousNavigation: Navigation | null;
     trigger: 'imperative' | 'popstate' | 'hashchange';
 }

packages/router/src/router.ts

@@ -274,7 +274,7 @@ export interface Navigation {
    * The target URL passed into the `Router#navigateByUrl()` call before navigation. This is
    * the value before the router has parsed or applied redirects to it.
    */
-  initialUrl: string|UrlTree;
+  initialUrl: UrlTree;
   /**
    * The initial target URL after being parsed with `UrlSerializer.extract()`.
    */
@@ -650,7 +650,7 @@ export class Router {
                      tap(t => {
                        this.currentNavigation = {
                          id: t.id,
-                         initialUrl: t.currentRawUrl,
+                         initialUrl: t.rawUrl,
                          extractedUrl: t.extractedUrl,
                          trigger: t.source,
                          extras: t.extras,