[flexiglass] Adds logging reason in QS view-model

Missed this in code review on ag/34026665. Having good logging reasons
for scene/overlay changes in Flexiglass is crucial for debugging later
on.

Bug: 420960164
Test: not tested, logging change only
Flag: com.android.systemui.scene_container
Change-Id: Id441cb41f82534a89fa2079f5c2529016a7e7454