Auto merge of #13589 - splav:SVGElement#12974, r=pcwalton,Ms2ger

Support SVG element

<!-- Please describe your changes on the following line: -->
minimal SVG element implementation
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12974 (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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tests/wpt/mozilla/meta/MANIFEST.json

@@ -6294,6 +6294,18 @@
             "url": "/_mozilla/mozilla/sslfail.html"
           }
         ],
+        "mozilla/svg/svg.html": [
+          {
+            "path": "mozilla/svg/svg.html",
+            "references": [
+              [
+                "/_mozilla/mozilla/svg/svg_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/mozilla/svg/svg.html"
+          }
+        ],
         "mozilla/table_valign_bottom.html": [
           {
             "path": "mozilla/table_valign_bottom.html",
@@ -20040,6 +20052,18 @@
           "url": "/_mozilla/mozilla/sslfail.html"
         }
       ],
+      "mozilla/svg/svg.html": [
+        {
+          "path": "mozilla/svg/svg.html",
+          "references": [
+            [
+              "/_mozilla/mozilla/svg/svg_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/mozilla/svg/svg.html"
+        }
+      ],
       "mozilla/table_valign_bottom.html": [
         {
           "path": "mozilla/table_valign_bottom.html",

tests/wpt/mozilla/meta/mozilla/svg/svg.html.ini

@@ -0,0 +1,3 @@
+[svg.html]
+    type: reftest
+    prefs: [dom.svg.enabled:true]