Fix window clipped in three-button-nav on phone factors

Since three-button-nav is transparent on phone factors, the bottom insets should not be clipped.

Bug: 373544911
Test: Manual, i.e. verifying that the window clipping is correct in all combinations of (tablet, phone) x (three-button--nav, gesture-nav)
Flag: com.android.window.flags.predictive_back_three_button_nav
Change-Id: Ie15b899a3e79514976868ff574faf1d02816822f