[idd] stop using IddCxMonitorUpdateModes(2)

While it would make much more sense to use these then a full replug to
change modes, Microsoft have not properly implemented the API to clear
the cached monitor mode states internally, making these calls useless.

Revert to just replugging the device on mode change

idd/LGIdd/CD3D12Device.h

@@ -69,6 +69,11 @@ struct CD3D12Device
     InitResult Init(CIVSHMEM &ivshmem, UINT64 &alignSize);
     void DeInit();
 
+    // Wait for all command queues to finish in-flight GPU work and run their
+    // completion callbacks. Used at swap-chain teardown so no callback touches
+    // resources we are about to release.
+    void WaitForIdle();
+
     ComPtr<ID3D12Device3> GetDevice() { return m_device; }
     ComPtr<ID3D12Heap   > GetHeap() { return m_ivshmemHeap; }
     bool IsIndirectCopy() { return m_indirectCopy; }