ActivityManagerService: make bluetooth actually persistent

com.android.bluetooth was being marked as a persistent service in terms
of OOM adjustment, but it was only being marked as important foreground for
scheduling reasons. Make sure that persistent services are correctly
marked as persistent for the purposes of scheduling too.

bug 78197570
Test: dumpsys activity

Change-Id: Ieb2fe4253cac1202bd94a42356bb32f9e77b5637