Add tracing for setEdgeBackPlugin

It seems this happens at every unfold, and still takes most of the taskbar initialization time due to `setLayoutParam` when the edge back plugin is set.

This trace will make it more easily visible in traces.

Bug: 219035565
Test: Checked perfetto traces for the new sections to be visible
Change-Id: I74e793467eb37705b2647d0ea9c64bd7b5191d9e