Handle renamed VREvent_ChaperoneRoomSetupFinished in OpenVR 2.12

Valve helpfully renamed `VREvent_ChaperoneRoomSetupFinished` in the latest release, opening this as a reminder that it will need to be renamed on our side as well next time we update OpenVR. Probably not worth maintaining backward compatibility since we haven't released 2.0 yet.

https://github.com/ValveSoftware/openvr/blame/9ebbda4af0da163b0606c8b88da4cde6bb3b85f0/headers/openvr.h#L966