Fix fling back behaviour for CrossActivityBackAnimation

It needs to be ensured that the surfaces are arranged correctly at least once before starting the post commit part of the back animation. Otherwise the post commit part of the animation will pick up a wrong starting point of the involved surfaces.

Bug: 309117413
Test: Manual, i.e. verifying that fling back behaves correctly on device
Change-Id: I3fcd230b9b7d4d2b115fdcdc4d301321fa1fb8d2