[WDF] Add Windows Driver Framework files

Takern from Microsoft GitHub repo:
d9c6040fe9

Licensed under MIT

sdk/lib/drivers/wdf/shared/irphandlers/pnp/um/eventqueueum.cpp

@@ -0,0 +1,77 @@
+/*++
+
+Copyright (c) Microsoft. All rights reserved.
+
+Module Name:
+
+    EventQueueUm.cpp
+
+Abstract:
+
+    This module implements user mode specific functionality of event queue
+
+    This functionality needed to be separated out since the KM portion takes
+    a reference on driver object because KM MxWorkItem::_Free does not wait for
+    callback to return (i.e. rundown synchronously).
+
+    MxWorkItem::_Free in UM currently waits for callback to return (i.e. runs
+    down synchronously) hence does not need a reference on driver/devstack
+    object (see comments on top of MxWorkItemUm.h file).
+
+    In future if UM work-item is made similar to km workitem, UMDF may need to
+    ensure that modules stay loaded, though the mechanism to ensure that would
+    likely be different from a reference on the driver. It would likely be a
+    reference on the devicestack object.
+
+Environment:
+
+    User mode only
+
+Revision History:
+
+
+
+
+--*/
+
+#include "pnppriv.hpp"
+
+VOID
+FxWorkItemEventQueue::QueueWorkItem(
+    VOID
+    )
+{
+    //
+    // In user mode WorkItem::_Free waits for workitem callbacks to return
+    // So we don't need outstanding reference on driver object or the devstack
+    //
+
+    m_WorkItem.Enqueue(
+        (PMX_WORKITEM_ROUTINE) _WorkItemCallback,
+        (FxEventQueue*) this);
+}
+
+VOID
+FxWorkItemEventQueue::_WorkItemCallback(
+    __in MdDeviceObject DeviceObject,
+    __in PVOID Context
+    )
+/*++
+
+Routine Description:
+    This is the work item that attempts to run the machine on a thread
+    separate from the one the caller was using.  It implements step 9 above.
+
+--*/
+{
+    FxWorkItemEventQueue* This = (FxWorkItemEventQueue*) Context;
+
+    UNREFERENCED_PARAMETER(DeviceObject);
+
+    //
+    // In user mode WorkItem::_Free waits for workitem callbacks to return
+    // So we don't need outstanding reference on driver object
+    //
+
+    This->EventQueueWorker();
+}