Adjust conditions to hold onto a task's dim

Check if task is translucent for transition to avoid having a closing
activity releasing its dimmer prematurely. This was causing the task's
dim being abandoned in favor of the ancestor's one, creating visible
issues.

Bug: 329233513
Test: verified with repro steps in the bug
Change-Id: Ib54c7b81816f14d3b9e9c634483ec07a12e590a9