Don't dispatch animation callbacks while hiding transient bar

When transient bars are hiding, the hiding animation is played at the
client side. Any app shouldn't know the transient state regardless of
showing or hiding. Otherwise, the app might react to it and cause the
screen flickering.

This CL skips dispatching animation callbacks while hiding transient
bar.

Fix: 385886995
Flag: EXEMPT bugfix
Test: atest ImeInsetsSourceConsumerTest InsetsAnimationControlImplTest
      InsetsSourceConsumerTest
Change-Id: Id8776621108d46bdbfa29447880e18a757997804