LibWeb: Rename CSS::StyleResolver => StyleComputer

Resolved style is a spec concept that refers to the weird mix of
computed style and used style reflected by getComputedStyle().

The purpose of this class is to produce the *computed* style for a given
element, so let's call it StyleComputer.

Userland/Libraries/LibWeb/HTML/HTMLLabelElement.cpp

@@ -21,7 +21,7 @@ HTMLLabelElement::~HTMLLabelElement()
 
 RefPtr<Layout::Node> HTMLLabelElement::create_layout_node()
 {
-    auto style = document().style_resolver().resolve_style(*this);
+    auto style = document().style_computer().compute_style(*this);
     if (style->display() == CSS::Display::None)
         return nullptr;