Libraries: Use default constructors/destructors in LibWeb

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Userland/Libraries/LibWeb/Layout/TextNode.cpp

@@ -21,9 +21,7 @@ TextNode::TextNode(DOM::Document& document, DOM::Text& text)
     set_inline(true);
 }
 
-TextNode::~TextNode()
-{
-}
+TextNode::~TextNode() = default;
 
 static bool is_all_whitespace(StringView string)
 {