Fully support <input type=color> (#36992)

This change adds a shadow-tree widget for `<input type=color>` elements.
It also involves some changes to the way layout interacts with the DOM,
because currently all `input` and `textarea` elements are rendered as
plain text and their descendants are ignored. This obviously doesn't
work for `<input type={color, date, range, etc}>`.


![image](https://github.com/user-attachments/assets/4f16c3b0-1f79-4095-b19d-1153f5853dd5)

<details><summary>HTML used for the screenshot above</summary>

```html
<input type=color>
```

</details>



Testing: I doubt that this affects WPT tests, because the appearance and
behaviour of the widget is almost entirely unspecified.

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/script/layout_dom/node.rs

@@ -96,6 +96,10 @@ impl<'dom> ServoLayoutNode<'dom> {
             .map(LayoutDom::upcast)
             .map(ServoLayoutElement::from_layout_js)
     }
+
+    pub fn is_text_input(&self) -> bool {
+        self.node.is_text_input()
+    }
 }
 
 impl style::dom::NodeInfo for ServoLayoutNode<'_> {