fix(Router): replace state when normalized path is equal to current normalized path

Make sure the same path is not added multiple times to the history.
It is replacing the state, instead of skipping it completely,
because the current path in the browser might not be normalized,
while the given one is normalized.

Closes #7829

Closes #7897

modules/@angular/common/src/location/location.ts

@@ -63,6 +63,13 @@ export class Location {
    */
   path(): string { return this.normalize(this.platformStrategy.path()); }
 
+  /**
+   * Normalizes the given path and compares to the current normalized path.
+   */
+  isCurrentPathEqualTo(path: string, query: string = ''): boolean {
+    return this.path() == this.normalize(path + Location.normalizeQueryParams(query));
+  }
+
   /**
    * Given a string representing a URL, returns the normalized URL path without leading or
    * trailing slashes