Tie prediction text to all apps interpolator

Now floating headers get 2 interpolators: one for the header content
itselt, and one for the all apps content that follows. That way, they
can choose to intperolate part of their content as if it were part of
all apps instead of the header. Currently, we do this to animate
predicted icons quickly, followed by the all apps icons, predictions
text, all apps scrollbar, and all apps divider as you continue swiping.

Bug: 132455160
Change-Id: Ib3e373c291e174e1306a53854d0ad4dc29eb4b76