servo: Merge #11616 - Add support for navigating by a delta (from cbrewster:navigation_delta); r=asajeffrey

<!-- Please describe your changes on the following line: -->
This adds support for passing a delta with `NavigationDirection`. This will be used with `history.go`

r? @asajeffrey

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because I am unsure how to write a test for this

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Source-Repo: https://github.com/servo/servo
Source-Revision: a80767993b6b2b885dfac9666f16fb1e1649ac99

servo/components/script/dom/htmliframeelement.rs

@@ -468,12 +468,12 @@ impl HTMLIFrameElementMethods for HTMLIFrameElement {
 
     // https://developer.mozilla.org/en-US/docs/Web/API/HTMLIFrameElement/goBack
     fn GoBack(&self) -> ErrorResult {
-        Navigate(self, NavigationDirection::Back)
+        Navigate(self, NavigationDirection::Back(1))
     }
 
     // https://developer.mozilla.org/en-US/docs/Web/API/HTMLIFrameElement/goForward
     fn GoForward(&self) -> ErrorResult {
-        Navigate(self, NavigationDirection::Forward)
+        Navigate(self, NavigationDirection::Forward(1))
     }
 
     // https://developer.mozilla.org/en-US/docs/Web/API/HTMLIFrameElement/reload