Save PackageDexUsage on PMS shutdown

This ensures that we persist the in memory data between restarts (makes
testing much easier).

Bug: 64151900
Test: Manual, flash + restart + check the dex usage file

(cherry picked from commit 6ef7f0b8c6e72e849a220513425a9fd37804af90)

Change-Id: I7bd99fc03c3a40cbbf5d615886f857b5f84f438c
3 files changed