LibWeb: Update Selection.collapse algorithm

Author: https://github.com/HolonProduction 🔰
Commit: https://github.com/LadybirdBrowser/ladybird/commit/94230acf287
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1252

Tests/LibWeb/Text/expected/collapse-selection-inside-shadow-root.txt

@@ -0,0 +1,6 @@
+   null
+null
+button1
+button1
+button2
+button2

Tests/LibWeb/Text/input/collapse-selection-inside-shadow-root.html

@@ -0,0 +1,35 @@
+<script src="include.js"></script>
+<button id="button1"></button>
+<div id="root"></div>
+<script>
+    function printSelectionNodes(selection) {
+        if (selection.anchorNode) {
+            println(`${selection.anchorNode.id}`);
+        } else {
+            println(`${selection.anchorNode}`);
+        }
+        if (selection.focusNode) {
+            println(`${selection.focusNode.id}`);
+        } else {
+            println(`${selection.focusNode}`);
+        }
+    }
+
+    test(() => {
+        printSelectionNodes(document.getSelection());
+
+        const button1 = document.querySelector("#button1");
+        document.getSelection().collapse(button1);
+
+        printSelectionNodes(document.getSelection());
+
+        const rootElement = document.getElementById("root");
+        const shadowRoot = rootElement.attachShadow({ mode: "open" });
+        const button2 = document.createElement("button");
+        button2.id = "button2";
+        shadowRoot.appendChild(button2);
+        document.getSelection().collapse(button2);
+
+        printSelectionNodes(document.getSelection());
+    });
+</script>

Userland/Libraries/LibWeb/Selection/Selection.cpp

@@ -183,8 +183,8 @@ WebIDL::ExceptionOr<void> Selection::collapse(JS::GCPtr<DOM::Node> node, unsigne
         return WebIDL::IndexSizeError::create(realm(), "Selection.collapse() with offset longer than node's length"_fly_string);
     }
 
-    // 3. If node's root is not the document associated with this, abort these steps.
-    if (&node->root() != m_document.ptr())
+    // 3. If document associated with this is not a shadow-including inclusive ancestor of node, abort these steps.
+    if (!m_document->is_shadow_including_inclusive_ancestor_of(*node))
         return {};
 
     // 4. Otherwise, let newRange be a new range.