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.

test/tests/StringTest.cpp

@@ -17,6 +17,8 @@
 #include <tuple>
 #include <utility>
 
+using namespace OpenRCT2;
+
 using TCase = std::tuple<std::string, std::string, std::string>;
 
 class StringTest : public testing::TestWithParam<TCase>