Let taskbar can trigger insets resize animation

All the system bar can trigger insets resize animation before, but some
sources might not have the resize animation. The framework now will only
trigger insets resize animation for sources which apply
FLAG_ANIMATE_RESIZING. So this CL applies the flag for gesture taskbar
because it can toggle its size via "Always show Taskbar"

Bug: 291562764
Flag: NA
Test: Fold and unfold a foldable device and ensure that won't create
      InsetsResizeAnimationRunner.
Merged-In: I0d915422d160a81f12c3992ffe53200fd957f6d7
Change-Id: I0d915422d160a81f12c3992ffe53200fd957f6d7