Light Sampling MIS Is Incorrect when using Multiple Lights

[Twinklebear]

Opening this as a reminder to myself and note to others, the second MIS step for lights is not correct if there are multiple lights in the scene (e.g. here for DXR). It should "trace" the ray and try to intersect all the lights to see which is hit.

However it sounds like this can also be improved by just using the path continuation ray as the "second MIS" sample, rather than having to trace two shadow rays. Eventually I'll move ChameleonRT to use this approach.