Make an AnrTimer flag non-read-only

Use a read/write flag to connect JobService to AnrTimer.  The previous
flag was fixed-read-only, which is not needed, and which prevents the
flag from entering partial trunk-food.  The previous flag cannot be
changed because it has already been seen by gantry.  Therefore a new
flag will be created.

Flag: com.android.server.utils.anr_timer_for_job_service
Bug: 408440679
Test: atest
 * FrameworksMockingServicesTests_com_android_server_job
 * FrameworksServicesTests:AnrTimerTest
Change-Id: I4c17f599e1b567f758ac52890a1f3128badd8cbe