Blend Space Graph node doesn't display fast path icon

Because SGraphNodeBlendSpaceGraph inherits from SGraphNodeK2Composite rather than UAnimGraphNode_Base as with most anim nodes, we aren't able to make the check as to whether the node is fast-path compliant or not in SGraphNodeBlendSpaceGraph::GetOverlayWidgets.

1. Create an anim blueprint
2. Drop in a BlendSpace node (not a Blendspace Player node)
3. Hook up the input pins on the node to a couple of bp variables and compile the graph
   1. Note how the fast path icon isn't displayed despite the input properties being taken directly from bp variables
   2. This contrasts to a Blendspace Player node which will display the fast path icon