Update Lottie animations in Back gesture tutorial

Based on UXR feedback, the animations for the back gesture tutorial
changed to start with displaying the thumb illustrating the back gesture
first. This change replaces the existing Lottie animations for the
new ones.

Flag: ENABLE_NEW_GESTURE_NAV_TUTORIAL
Fix: 285640701
Test: Manually went through the tutorial for handheld, foldable, and
tablet devices and verified the new animation plays properly.

Change-Id: Ifcc5fb61521825ea55f0b959ad1c112013a20f9c