Bug 1702978 - Reduce springiness of the overscroll snapback animation. r=botond

This makes the snapback less aggressive, and feels more like Safari to me.
Reducing the stiffness makes the animation take longer to complete.
To counteract the longer time, I've also reduced the damping a little bit;
reducing the damping makes the animation complete a little more quickly.

Depends on D110845

Differential Revision: https://phabricator.services.mozilla.com/D110846

modules/libpref/init/StaticPrefList.yaml

@@ -598,12 +598,12 @@
 
 - name: apz.overscroll.spring_stiffness
   type: AtomicFloat
-  value: 400
+  value: 200
   mirror: always
 
 - name: apz.overscroll.damping
   type: AtomicFloat
-  value: 1.2
+  value: 1.1
   mirror: always
 
 - name: apz.overscroll.max_velocity