Rewrite scheduler context switch code (#1786)

* Rewrite scheduler context switch code

* Fix race in UnmapIpcRestorePermission

* Fix thread exit issue that could leave the scheduler in a invalid state

* Change context switch method to not wait on guest thread, remove spin wait, use SignalAndWait to pass control

* Remove multi-core setting (it is always on now)

* Re-enable assert

* Remove multicore from default config and schema

* Fix race in KTimeManager

Ryujinx.HLE/HOS/Kernel/Threading/KThreadContext.cs

@@ -0,0 +1,19 @@
+using System.Threading;
+
+namespace Ryujinx.HLE.HOS.Kernel.Threading
+{
+    class KThreadContext
+    {
+        private int _locked;
+
+        public bool Lock()
+        {
+            return Interlocked.Exchange(ref _locked, 1) == 0;
+        }
+
+        public void Unlock()
+        {
+            Interlocked.Exchange(ref _locked, 0);
+        }
+    }
+}