[incremental/pm] app states and transitions

Based on go/incremental-states-design with basic
setter/getters.

Defines IncrementalStates class which handles state transitions.

New (internal) Intent actions: PACKAGE_FULLY_LOADED, PACKAGE_STARTABLE,
PACKAGE_UNSTARTABLE.

BUG: 168043976
Test: unit tests
Change-Id: I7b0ec2dd9f028ee620a9307a1e71ddf12ea5a9af