SilkFx BackgroundBlur: handle rotation properly

This fix to a test app assists in smoke testing the linked bug fix.

The bug was that the progress listener was set up on the view before the
ViewRoot is attached to the Window. During onRestoreInstanceState, view
progress levels were restored, triggering APIs to set the background &
blur-behind levels.

We should only have these listeners called after onAttachedToWindow.

Bug: 391463550
Test: manual by opening the app and rotating in full/split screen
Flag: EXEMPT test app that is not used in production
Change-Id: I74a33604715bcc5ac49a279e8edfe975550e79a1