If RecentsView is empty when starting quickswitch, listen for tasks to load

When first doing quick switch, RecentsView might be empty but tasks subsequently
load. In that case, we can update our animators to have the correct scale etc.

Test: From home, toggle dark theme or RTL from quick setting tiles,
then quick switch; ensure RecentsView comes in scaled up.

Bug: 126596417
Change-Id: I28d79455431b1da634372d6f31182406aa24cd06