Clear idle state of destroyed activity

This is mainly for when the activity process is died in background:
AR#handleAppDied -> cleanUp -> setState(DESTROYED, "cleanUp")

This prevents allResumedActivitiesIdle from misjudging idle state
when cold launching the died activity again.

Bug: 356522395
Flag: EXEMPT bugfix
Test: atest ActivityRecordTests# \
            testDestroyImmediately_hadApp_notFinishing
Test: Launch app A, launch app B. Return to home.
      Use "adb shell kill -9 $pid" to kill B.
      Enter split-screen including A and B.
      The launch mode power should end after B is started.
Change-Id: Ib1cf28c71cfb2fb8ff64cc42fffd2003dce727f4