Fix top app unable to start activity due to BAL

Application starts activity in Application#onCreate could be
blocked by BAL due to identifying a visible activity from
that app is not possible because the application process
has not yet fully attached.

Bug: 425287771
Test: BackgroundActivityStartControllerExemptionTests
Flag: EXEMPT bugfix
Change-Id: I275f990b255820fa0e9eca944140d2da2c21edcd