Refactoring of AppOps pullers.

- adjusts sampling ratio in the same run if dimensions limit is reached
- for AppOps atom turns on sampling if dimensions limit is reached
- moved execution off main executor
- sampling ratio estimation is no longer performed during first pull
- hashing function optimized for speed

Bug: 143519689
Test: stats_testdrive 10060 & 10075, atest UidAtomTests#testAppOps

Change-Id: Ie925608a4c9484f1300ae7cda1ed7b037858114f