Add 200 ms delay for predictive back animation in 3-button-nav

Bug: 373544911
Test: Manual, i.e. verifying that regular clicks on the back button don't trigger predictive back animations but long presses do
Flag: com.android.window.flags.predictive_back_three_button_nav
Change-Id: I148bae8f09fa9b6d17fd929067b02175882115a3