Use IoThread handler for AppOpsService background/IO work

AppOpsService has been using AMS handler so far for most of
its work, AMS handler is passed in AppOpsService constructor.
We shouldn't be using AMS handler for app ops disk io,
IO handler is now used for disk read/writes.

Bug: 394380603
Test: presbumit
Test: manual tested the device by visiting
privacy dashboard and permission timeline page
FLAG: EXEMPT bug fix

Change-Id: I2933e80a3b95bd34eff34abc1b51dd50ec43ce81