Fix for split animation

While splitting focus task, there is a timing issue of focus task being animated first and then small tiles.
This CL fixes that makes animation smooth i.e. animate stage task(focus task) and other small tiles together.

 Also refactored animationStartProgress and animationEndProgress initialisation by adding "if/else" for readability.

Test: Manual.Split focus task.(RTL as well)
Fix: 383417963
Flag: com.android.launcher3.enable_large_desktop_windowing_tile
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:ff076f85d6e3c9f537ea022ee15b10c7a1e97225)
Merged-In: I7b8c651d91168802b930fdeac62e762a2be9dbe9
Change-Id: I7b8c651d91168802b930fdeac62e762a2be9dbe9