Adopt existing namespaces into OpenRCT2 namespace (#22368)

* Put all of TitleSequenceManager into the same namespace

* Move RideConstructionState into the OpenRCT2 namespace

* Adopt existing namespaces into OpenRCT2 namespace

This adds `using namespace OpenRCT2` to compilation units where appropriate,
as a means to get the codebase to compile until these units have been placed
in a namespace of their own.

src/openrct2/object/ObjectFactory.cpp

@@ -48,6 +48,8 @@
 #include <memory>
 #include <unordered_map>
 
+using namespace OpenRCT2;
+
 struct IFileDataRetriever
 {
     virtual ~IFileDataRetriever() = default;
@@ -211,7 +213,7 @@ public:
     }
 };
 
-namespace ObjectFactory
+namespace OpenRCT2::ObjectFactory
 {
     /**
      * @param jRoot Must be JSON node of type object
@@ -591,4 +593,4 @@ namespace ObjectFactory
         }
         return result;
     }
-} // namespace ObjectFactory
+} // namespace OpenRCT2::ObjectFactory