Detach stale IME leash for orientation change with gesture navigation

Once computeImeTarget is called that updates mImeLayeringTarget, the
IME surface container will reparent to the new target when starting
input connection (reportStartInput).

When there is an orientation change, the insets source control may
take time to be ready (drawn). If IME surface container is reparented
before the new insets control target updates the insets leash, the
IME in previous rotation will show on the app in new rotation.
e.g.
 Top: PortraitApp (visible)
        > ImeContainer
          > Ime leash for LandscapeApp
      LandscapeApp (invisible)
 And LandscapeApp may still update visibility/position to the leash.
So simply detach the leash to avoid showing inconsistent content.
The new leash for PortraitApp will be created once IME is drawn.

Bug: 335204769
Test: Launch chrome, click search bar to show IME.
      Rotate device to landscape.
      Swipe from landscape to portrait home.
      A landscape IME should not flicker on portrait home.
Change-Id: Iac6edc569330b0d89c0ee03fbd1143573babe228