Fix issue where Assistant could be invoked at the same time as all apps

issue 132366412

-> First, we shouldn't accept flings when the delegate has intercepted. This prevents any situation
   where both are triggered.

-> Modified the slop to be the standard 8dp. This acts as a standalone fix because
   it means that there are no situations where we cross all apps slop before assistant slop.
   ie. in a purely vertical gesture from the corner, without this change, it's possible to trigger
   all apps instead of Assistant.

Change-Id: I39e3d8a525e165024399d9802d4cc1d7ae329ee6