[ntcore] Provide mechanism to reset internals of NT instance (#4653)

ntcore/src/main/native/include/ntcore_cpp.h

@@ -348,6 +348,13 @@ NT_Inst GetDefaultInstance();
  */
 NT_Inst CreateInstance();
 
+/**
+ * Reset the internals of an instance. Every handle previously associated
+ * with this instance will no longer be valid, except for the instance
+ * handle.
+ */
+void ResetInstance(NT_Inst inst);
+
 /**
  * Destroy an instance.
  * The default instance cannot be destroyed.