Move non-output to new CppUtils namespace

We prefer to have the Outputs directory contain just one file or
namespace per output module, so we'll move all C++-related stuff to a
new CppUtils namespace instead.

Il2CppInspector.CLI/Program.cs

@@ -9,7 +9,7 @@ using System.Linq;
 using CommandLine;
 using Il2CppInspector.Reflection;
 using Il2CppInspector.Outputs;
-using Il2CppInspector.Outputs.UnityHeaders;
+using Il2CppInspector.CppUtils.UnityHeaders;
 
 namespace Il2CppInspector.CLI
 {