LibWeb: Calculate length for all CharacterData type nodes correctly

We now ensure that `Node::is_character_data()` returns true for all
nodes of type character data.

Previously, calling `Node::length()` on `CDataSection` or
`ProcessingInstruction` nodes would return an incorrect value.

Tests/LibWeb/Text/expected/DOM/Range-containing-CDATASection.txt

@@ -0,0 +1 @@
+range start offset: 0, end offset: 3

Tests/LibWeb/Text/input/DOM/Range-containing-CDATASection.html

@@ -0,0 +1,11 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const xmlDocument = new DOMParser().parseFromString(`<xml></xml>`, "application/xml");
+        const cdata = xmlDocument.createCDATASection("DATA");
+        const range = xmlDocument.createRange();
+        range.setStart(cdata, 0);
+        range.setEnd(cdata, 3);
+        println(`range start offset: ${range.startOffset}, end offset: ${range.endOffset}`);
+    });
+</script>

Userland/Libraries/LibWeb/DOM/Node.h

@@ -8,6 +8,7 @@
 
 #include <AK/Badge.h>
 #include <AK/FlyString.h>
+#include <AK/GenericShorthands.h>
 #include <AK/JsonObjectSerializer.h>
 #include <AK/RefPtr.h>
 #include <AK/TypeCasts.h>
@@ -69,7 +70,7 @@ class Node : public EventTarget {
     bool is_document() const { return type() == NodeType::DOCUMENT_NODE; }
     bool is_document_type() const { return type() == NodeType::DOCUMENT_TYPE_NODE; }
     bool is_comment() const { return type() == NodeType::COMMENT_NODE; }
-    bool is_character_data() const { return type() == NodeType::TEXT_NODE || type() == NodeType::COMMENT_NODE; }
+    bool is_character_data() const { return first_is_one_of(type(), NodeType::TEXT_NODE, NodeType::COMMENT_NODE, NodeType::CDATA_SECTION_NODE, NodeType::PROCESSING_INSTRUCTION_NODE); }
     bool is_document_fragment() const { return type() == NodeType::DOCUMENT_FRAGMENT_NODE; }
     bool is_parent_node() const { return is_element() || is_document() || is_document_fragment(); }
     bool is_slottable() const { return is_element() || is_text() || is_cdata_section(); }