[Bouncer] Reset y translation and alpha

When doing the appear animation, sometimes, the animation will not
complete. I am unable to repro reliably, but I have experienced the
behavior more than 3 times, and QA has seen it too.

I'm thinking that this code change will fix the issue, but it's not
guaranteed.

Bug: 228886154
Test: Manual
Change-Id: Ie6b138468e3f8ef3e27bc2e3249c0de13709ed57