Make all swipe transitions irreversible

This CL makes all transitions irreversible, i.e. it's impossible to
start a swipe transition A => B then reverse to A => C by simply
changing direction without lifting the finger. This feature was mostly
useful for the Shade scene, where going Shade => Gone/LS then reverse to
Shade => QS was nice to have.

Bug: 379281707
Test: Manual, played with flexiglass on
Flag: com.android.systemui.scene_container
Change-Id: I65b91ec31d0b7deaa1c32b3d70ca6ac4df9b5553