Augment diskstats dumpsys to have categorization and apps.

This adds a new service which opportunistically saves the
file system categorization information and the app sizes. This
information is fetched during a diskstats dumpsys call from a file
stored on the disk. This allows us to keep the dumpsys running quickly
while adding information which is costly to calculate.

Bug: 32207207
Test: System server instrumentation tests
Change-Id: Id59e84b9ad38a9debf3e46e5133ef06f7353829d