FIX: Further improvements to `//` handling (#28211)

Followup to f70a65ea02

1. Update a second regex in `routeTo` to avoid stripping domain/protocol from middle of string

2. Update `URL.handleURL` to strip double-slashes in paths, before calling the ember router. This mimics what Ember does on initial page-load

Additional tests are added for both

app/assets/javascripts/discourse/app/lib/url.js

@@ -235,7 +235,7 @@ class DiscourseURL extends EmberObject {
 
     const oldPath = this.routerService.currentURL;
 
-    path = path.replace(/(https?\:)?\/\/[^\/]+/, "");
+    path = path.replace(/^(https?\:)?\/\/[^\/]+/, "");
 
     // handle prefixes
     if (path.startsWith("/")) {
@@ -437,6 +437,10 @@ class DiscourseURL extends EmberObject {
       elementId = split[1];
     }
 
+    // Remove multiple consecutive slashes from path. Same as Ember does on initial page load:
+    // https://github.com/emberjs/ember.js/blob/8abcd000ee/packages/%40ember/routing/history-location.ts#L146
+    path = path.replaceAll(/\/\/+/g, "/");
+
     const transition = this.routerService.transitionTo(path);
 
     transition._discourse_intercepted = true;

app/assets/javascripts/discourse/tests/acceptance/url-test.js

@@ -0,0 +1,19 @@
+import { currentURL, settled, visit } from "@ember/test-helpers";
+import { test } from "qunit";
+import DiscourseURL from "discourse/lib/url";
+import { acceptance } from "discourse/tests/helpers/qunit-helpers";
+
+acceptance("DiscourseURL", function () {
+  test("handleURL strips multiple slashes", async function (assert) {
+    await visit("/");
+
+    DiscourseURL.handleURL("/t//280");
+    await settled();
+
+    assert.strictEqual(
+      currentURL(),
+      "/t/internationalization-localization/280"
+    );
+    assert.dom("#topic-title").exists();
+  });
+});

app/assets/javascripts/discourse/tests/unit/lib/url-test.js

@@ -141,11 +141,17 @@ module("Unit | Utility | url", function (hooks) {
       "it strips the protocol and domain when protocol-less"
     );
 
-    DiscourseURL.routeTo("https://example.com//foo4");
+    DiscourseURL.routeTo("https://example.com/t//1");
     assert.ok(
-      DiscourseURL.handleURL.calledWith(`//foo4`),
+      DiscourseURL.handleURL.calledWith(`/t//1`),
       "it does not strip double-slash in the middle of urls"
     );
+
+    DiscourseURL.routeTo("/t//2");
+    assert.ok(
+      DiscourseURL.handleURL.calledWith(`/t//2`),
+      "it does not strip double-slash in the middle of urls, even without a domain"
+    );
   });
 
   test("routeTo does not rewrite routes started with /my", async function (assert) {