Animate window blur between hub and gone

This change introduces animation of the window blur which blurs the
background behind lockscreen widgets. This makes the transition between
hub and gone (e.g. edit mode) more smooth.

Test: manual; see video in bug
Bug: 392889809
Flag: com.android.systemui.notification_shade_blur
Change-Id: Ibe262e20e9cc50d298ec56866139af2b5039afd8