Move related classes into AttributedOp

Move InProgressStartOpEvent, InProgressStartOpEventPool, and
OpEventProxyInfoPool into the AttributedOp class.

These are currently in AppOpsService, but are only ever used by
AttributedOp. Moving them reduces the amount of noise in AppOpsService.

Test: presubmit
Change-Id: Ic4e03b82c481c73914470d143c733a0ea243a72d