Fix Manage Windows alpha animation.

Sets initial alpha of icon views to 0. This prevents an animation bug
where icons would fully show, jump to 0 alpha, then animate to full.

Additionally, correctly applies delay to icon view alpha animation,
starting it slightly after the base view's animator.

Bug: 439604183
Test: Manual
Flag: EXEMPT, minor change
Change-Id: I97861f712b2072a6b0184a1d5a13bc6e538326e4