Implement a tear-down phase in otapreopt_chroot.

Collect the list of APEX packages activated by `otapreopt_chroot` and
deactivate them after executing `otapreopt` (in its own process).

Also share android::installd::Exec between `otapreopt` and
`otapreopt_chroot`.

This tear-down phase ensures loop devices associated during by
`otapreopt_chroot` are detached before `otapreopt_chroot` exits.

Test: m otapreopt_chroot
Test: A/B OTA update test (asit/dexoptota/self_full).
Bug: 113373927
Bug: 120796514
Change-Id: I236ac49bb698fb672e7a4f9de9903229e535e9c6