Make HLE disposable safely (#850)

* Make HLE disposable safely

This fix the oldest issue with the HLE code: the kernel side
disposability.

Changelog:

- Implement KProcess::UnpauseAndTerminateAllThreadsExcept, KThread::Terminate, KThread::TerminateCurrentProcess, KThread::PrepareForTermiation and the svc post handler accurately.
- Implement svcTerminateProcess and svcExitProcess. (both untested)
- Fix KHandleTable::Destroy not decrementing refcount of all objects stored in the table.
- Spawn a custom KProcess with the maximum priority to terminate every guest KProcess. (terminating kernel emulation safely)
- General system stability improvements to enhance the user's experience.

* Fix a typo in a comment in KProcess.cs

* Address gdk's comments

Ryujinx.HLE/HOS/Kernel/SupervisorCall/SvcHandler.cs

@@ -1,5 +1,6 @@
 using ARMeilleure.State;
 using Ryujinx.HLE.HOS.Kernel.Process;
+using Ryujinx.HLE.HOS.Kernel.Threading;
 using System;
 
 namespace Ryujinx.HLE.HOS.Kernel.SupervisorCall
@@ -29,6 +30,15 @@ namespace Ryujinx.HLE.HOS.Kernel.SupervisorCall
             ExecutionContext context = (ExecutionContext)sender;
 
             svcFunc(this, context);
+
+            PostSvcHandler();
+        }
+
+        private void PostSvcHandler()
+        {
+            KThread currentThread = _system.Scheduler.GetCurrentThread();
+
+            currentThread.HandlePostSyscall();
         }
     }
 }