Bound recents content alpha to 0 and 1

Now that we use OvershootInterpolator for the atomic recents animation,
it's possible to get alpha > 1. The drawable and text paint used in the
empty recents state doesn't handle this well, causing alpha to jump to 0
in this case. Instead, we'll just force it to clamp to 1 ourselves.

Bug: 80004542
Change-Id: Id0177caf63cd349f6f27c9dfaf0e8995447e70fc