Add API to track package changes

After any package install, removal or update, save the changed
package and update a global sequence number. At any point, apps
can query for the packages changed since a particular sequence
number.

If a package is changed multiple times, it is only included once
in the change list.

Bug: 33865505
Test: Create sample app to query for changes and see which packages are changed after performing certain operations
Change-Id: Ia4646035362b16a97110e05f3f909ce385b48428