Auto merge of #14367 - mrobinson:scroll-fragment-point, r=pcwalton

Reimplement scrolling to fragments

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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 fix #13736, #10753 (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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This reimplemntation of the feature uses ScrollRootIds to scroll
particular scrollable areas of the page.

Fixes #13736.
Fixes #10753.

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -6414,6 +6414,18 @@
             "url": "/_mozilla/mozilla/iframe/resize_after_load.html"
           }
         ],
+        "mozilla/simple_scroll_to_fragment.html": [
+          {
+            "path": "mozilla/simple_scroll_to_fragment.html",
+            "references": [
+              [
+                "/_mozilla/mozilla/simple_scroll_to_fragment_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/mozilla/simple_scroll_to_fragment.html"
+          }
+        ],
         "mozilla/sslfail.html": [
           {
             "path": "mozilla/sslfail.html",
@@ -21432,6 +21444,18 @@
           "url": "/_mozilla/mozilla/iframe/resize_after_load.html"
         }
       ],
+      "mozilla/simple_scroll_to_fragment.html": [
+        {
+          "path": "mozilla/simple_scroll_to_fragment.html",
+          "references": [
+            [
+              "/_mozilla/mozilla/simple_scroll_to_fragment_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/mozilla/simple_scroll_to_fragment.html"
+        }
+      ],
       "mozilla/sslfail.html": [
         {
           "path": "mozilla/sslfail.html",