[WDF] Add Windows Driver Framework files

Takern from Microsoft GitHub repo:
d9c6040fe9

Licensed under MIT

sdk/lib/drivers/wdf/shared/primitives/um/mxworkitemum.cpp

@@ -0,0 +1,66 @@
+/*++
+
+Copyright (c) Microsoft Corporation
+
+ModuleName:
+
+    MxWorkItemUm.cpp
+
+Abstract:
+
+    Work item callback thunk implementation for user mode
+
+    We need this thunk to wire the um callback to a mode agnostic work item
+    callback.
+
+Author:
+
+
+
+Revision History:
+
+
+
+--*/
+
+#include "Mx.h"
+
+VOID
+CALLBACK
+MxWorkItem::_WorkerThunk (
+    _Inout_ PTP_CALLBACK_INSTANCE Instance,
+    _Inout_opt_ PVOID Parameter,
+    _Inout_ PTP_WAIT Wait,
+    _In_ TP_WAIT_RESULT WaitResult
+    )
+{
+    MdWorkItem workItem = (MdWorkItem) Parameter;
+
+    UNREFERENCED_PARAMETER(Instance);
+    UNREFERENCED_PARAMETER(Wait);
+    UNREFERENCED_PARAMETER(WaitResult);
+
+    (*workItem->Callback)(
+        workItem->DeviceObject,
+        workItem->Context
+        );
+
+    return;
+}
+
+VOID
+MxWorkItem::WaitForCallbacksToComplete(
+    VOID
+    )
+{
+    Mx::MxAssert(NULL != m_WorkItem->WaitBlock);
+
+    //
+    // Wait for outstanding callbacks to complete.
+    //
+    WaitForThreadpoolWaitCallbacks(m_WorkItem->WaitBlock,
+                           FALSE  // donot cancel pending waits
+                           );
+
+}
+