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/CMakeLists.txt

@@ -31,9 +31,9 @@ set(SOURCES
     CSS/Screen.cpp
     CSS/Selector.cpp
     CSS/SelectorEngine.cpp
+    CSS/StyleComputer.cpp
     CSS/StyleInvalidator.cpp
     CSS/StyleProperties.cpp
-    CSS/StyleResolver.cpp
     CSS/StyleSheet.cpp
     CSS/StyleSheetList.cpp
     CSS/StyleValue.cpp