Adding logging to debug bubble drag failures

DragAndDismiss test is flaky. Bubble should be dragged to the dismiss
view, but dismiss view is not shown. And bubble is not dismissed. Add
some debug logging around drag events to help root cause the issue.

Bug: 417749498
Flag: EXEMPT adding logging, no behavior changes
Test: presubmit
Change-Id: Ia5447249b8d104d91cff33a021dea05669954eaa