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/EditorObjectSelectionSession.cpp

@@ -34,6 +34,8 @@
 #include <iterator>
 #include <vector>
 
+using namespace OpenRCT2;
+
 std::optional<StringId> _gSceneryGroupPartialSelectError;
 std::vector<uint8_t> _objectSelectionFlags;
 uint32_t _numSelectedObjectsForType[EnumValue(ObjectType::Count)];