Auto merge of #11934 - jdm:navigatefragment, r=emilio

Special-case setting location.hash to the empty string

This avoids endless redirect loops on facebook and makes us compliant with https://github.com/whatwg/html/pull/1318.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #10952
- [X] There are tests for these changes OR

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components/script/dom/location.rs

@@ -66,7 +66,10 @@ impl LocationMethods for Location {
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-location-hash
-    fn SetHash(&self, value: USVString) {
+    fn SetHash(&self, mut value: USVString) {
+        if value.0.is_empty() {
+            value = USVString("#".to_owned());
+        }
         self.set_url_component(value, UrlHelper::SetHash);
     }