Auto merge of #19803 - jonleighton:issue-19765, r=emilio

Implement Element::has_css_layout_box()

r? emilio

Here's my initial attempt to fix #19430. It seems surprisingly simple so I am wondering whether I have missed something! (Or maybe it just actually is quite simple...)

Some things I am unsure about:

1. The spec seems vague about what a [CSS layout box](https://drafts.csswg.org/cssom-view/#css-layout-box) actually is. Indeed it says: "The terms CSS layout box and SVG layout box are not currently defined by CSS or SVG."
2. One thing the spec *does* say explicitly is "For the purpose of the requirements in this specification, elements that have a computed value of the display property that is table-column or table-column-group must be considered to have an associated CSS layout box (the column or column group, respectively)." I am unclear about the relevance of this, since [overflow does not apply](https://drafts.csswg.org/css-overflow-3/#overflow-properties) to an [internal table element](https://drafts.csswg.org/css-display-3/#layout-specific-display). Therefore I haven't done anything about this explicitly, but maybe I'm missing some nuance.

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tests/wpt/metadata/MANIFEST.json

@@ -308101,6 +308101,12 @@
      {}
     ]
    ],
+   "css/cssom-view/scroll-no-layout-box.html": [
+    [
+     "/css/cssom-view/scroll-no-layout-box.html",
+     {}
+    ]
+   ],
    "css/cssom-view/scrollIntoView-shadow.html": [
     [
      "/css/cssom-view/scrollIntoView-shadow.html",
@@ -516726,6 +516732,10 @@
    "966ebff69f91c0ea92f4bc2f943df9ef9dc3bcf9",
    "testharness"
   ],
+  "css/cssom-view/scroll-no-layout-box.html": [
+   "8f423a757bd716c9c22e82fd2f35007d05982c08",
+   "testharness"
+  ],
   "css/cssom-view/scrollIntoView-shadow.html": [
    "3c4a18992105fd7bf19cbf29f0b6d80cb12ca98c",
    "testharness"