[threading] Change thread names to suit pthread

Shorten names to 16.
Rename Win32 to Windowing.
Shorten GraphicsSystem thread names due to 16 length limit of pthread.
Without this change, both show up as GraphicsSystem.
Remove redundant "Worker" and "Thread" from names.
Remove redundant thread handle from thread name.

src/xenia/gpu/command_processor.cc

@@ -73,7 +73,7 @@ bool CommandProcessor::Initialize(
         WorkerThreadMain();
         return 0;
       }));
-  worker_thread_->set_name("GraphicsSystem Command Processor");
+  worker_thread_->set_name("GPU Commands");
   worker_thread_->Create();
 
   return true;