Animate in desktop app select toast

Add an animation for the desktop app select toast.
Played when the toast is added to the screen.

Bug: 261234402
Test: have an app on desktop, swipe up to home, verify that the toast
  has an appear animation, per the spec
Test: when toast is visible, tap on cancel button, observe toast fades
  out
Test: when toast is visible, launch an app, verify toast fades out
Change-Id: I593d6c326d6d638f1bc06e8c6add31b0244e4cb5