A bug was introduced in https://github.com/videolan/libvlcsharp/pull/87 which would crash the CLR
when the cleanup callback was set. The issue was that the vmem plugin does not have a Stop concept,
only closed, in which it frees up a struct containing a pointer which is used later by LVS.

So for the cleanup callback only, revert to the previous code.

Closes videolan/LibVLCSharp#339

This reverts commit 6b2665fe.

Since cc890e45, the TFM for UWP was bumped. b883bd7c missed this
sample.

they use the steps to explain how to build the repro,
instead of just sharing the built repro.

Fix videolan/LibVLCSharp#537

Fixes Managed Debugging Assistant 'PInvokeStackImbalance'
A call to PInvoke function 'LibVLCSharp.WPF!LibVLCSharp.WPF.User32Wrapper::CreateWindowEx' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

Close videolan/LibVLCSharp#529