LibHTML: Get rid of the style tree

We now create a layout tree directly from the DOM tree.
This way we don't actually lose text nodes ^)

Libraries/LibHTML/CSS/StyleProperties.cpp

@@ -0,0 +1,22 @@
+#include <LibHTML/CSS/StyleProperties.h>
+
+void StyleProperties::set_property(const String& name, NonnullRefPtr<StyleValue> value)
+{
+    m_property_values.set(name, move(value));
+}
+
+Optional<NonnullRefPtr<StyleValue>> StyleProperties::property(const String& name) const
+{
+    auto it = m_property_values.find(name);
+    if (it == m_property_values.end())
+        return {};
+    return it->value;
+}
+
+Length StyleProperties::length_or_fallback(const StringView& property_name, const Length& fallback) const
+{
+    auto value = property(property_name);
+    if (!value.has_value())
+        return fallback;
+    return value.value()->to_length();
+}