Update PiP movement bounds on TaskBar inset change

The DisplayLayout#stableInsets was set according to navigation bar
height and not get updated when TaskBar becomes visible.

Video: http://recall/-/aaaaaabFQoRHlzixHdtY/dPuTSbBuAgjfyKiliwzo2Q
Bug: 198644965
Test: Open another app with PiP present and move it around, see Video
Test: atest WMShellUnitTests:PipControllerTest
Change-Id: I4db1446de0cb257e26d34985d294908cfe692967