Intern package names in AppOps historical data.

AppOps historical data contains many repeated packages names stored in
attribute values, increasing disk space and reading/writing time.

This change makes a trivial adjustment to write these package names
as "interned" values gives the serializer the option of writing the
package name once and then using a lightweight backreference for all
future instances.  Existing benchmarks show substantial CPU and disk
improvements when interning is enabled.

Bug: 171832118
Test: atest FrameworksServicesTests
Change-Id: I6d4a01e13caaf294aa6e015c528b909163dcae10