DynamicWind doesn't unregister proxy and leaks

FSkinnedSceneProxy's never get unregistered from the DynamicWind system

In FDynamicWindTransformProvider::UnregisterSceneProxy, there's an early out that says:

if (SkinningSceneExtProxy == nullptr || SkinningSceneExtProxy->GetTransformProviderId() != DynamicWindTransformProviderId)

This UnregisterSceneProxy is triggered by a OnDestroyRenderThreadResources delegate. By the time it reaches the if above, it has already destroyed the RenderThreadResources, which makes FInstancedSkinningSceneExtensionProxy::TransformProviderProxy null. Due to this, when SkinningSceneExtProxy->GetTransformProviderId() is called, it does not identify itself as being of DynamicWind kind, but instead if falls back to REF_POSE_TRANSFORM_PROVIDER_GUID, and due to this the UnregisterSceneProxy earlies out, disregarding any proxy that arrives here. To check, I added a breakpoint after this early out, and it's never triggered it (removing ISkMs with wind, reloading the level, etc.). I have added a fix that returns the TransformProviderId member directly for this specific check, without going through the TransformProviderProxy.

This means SkeletonLookup entries leak — the ReferenceCount is never decremented, bone data is never freed from the BoneDataAllocator, and entries accumulate

It appears FInstancedSkinningSceneExtensionProxy::TransformProviderId defaults to RefPoseProviderId in the constructor when !succeeded, can we just return TransformProviderId in FInstancedSkinningSceneExtensionProxy::GetTransformProviderId()?

Steps to Reproduce

• Create an ISkM with a DynamicWindSkeletalData assigned and a TransformProvider and a single instance, so that wind blows on it.
• Add a breakpoint in the FDynamicWindTransformProvider::UnregisterSceneProxy, after all early outs.
• Remove the ISkM, or simply reload the level. Notice how nothing never unregisters from it (at least in my case).