LibWeb: Move StackingContext from Layout/ to Painting/

The stacking context tree doesn't affect layout at all, so let's move
it into the Painting/ directory. I'm not sure yet if it's worth going
for a fullly separate painting tree. So far I'm thinking a stacking
context tree with pointers into the layout tree might be enough.

Libraries/LibWeb/CMakeLists.txt

@@ -94,7 +94,6 @@ set(SOURCES
     Layout/LayoutWidget.cpp
     Layout/LineBox.cpp
     Layout/LineBoxFragment.cpp
-    Layout/StackingContext.cpp
     LayoutTreeModel.cpp
     Loader/FrameLoader.cpp
     Loader/ImageLoader.cpp
@@ -103,6 +102,7 @@ set(SOURCES
     Loader/ResourceLoader.cpp
     Page.cpp
     PageView.cpp
+    Painting/StackingContext.cpp
     Parser/CSSParser.cpp
     Parser/Entities.cpp
     Parser/HTMLDocumentParser.cpp
@@ -113,7 +113,6 @@ set(SOURCES
     Parser/StackOfOpenElements.cpp
     StylePropertiesModel.cpp
     URLEncoder.cpp
-
     CSS/PropertyID.h
     CSS/PropertyID.cpp
     CSS/DefaultStyleSheetSource.cpp

Libraries/LibWeb/Layout/LayoutBox.h

@@ -29,7 +29,7 @@
 #include <AK/OwnPtr.h>
 #include <LibGfx/FloatRect.h>
 #include <LibWeb/Layout/LayoutNode.h>
-#include <LibWeb/Layout/StackingContext.h>
+#include <LibWeb/Painting/StackingContext.h>
 
 namespace Web {
 

Libraries/LibWeb/Layout/LayoutDocument.cpp

@@ -29,7 +29,7 @@
 #include <LibWeb/Layout/LayoutDocument.h>
 #include <LibWeb/Layout/LayoutImage.h>
 #include <LibWeb/Layout/LayoutWidget.h>
-#include <LibWeb/Layout/StackingContext.h>
+#include <LibWeb/Painting/StackingContext.h>
 
 namespace Web {