Improve dump of staged sessions in dumpsys

The dumpsys output for staged sessions is reformatted for active,
orphaned child and finalized sessions as follows:
1) Nested child sessions under parent
2) Parent sessions sorted by creation time
3) Nested child sessions sorted by creation time
4) Prefix before session number indicating session type

Bug: 193113385
Test: Install multiple staged sessions
Test: adb shell dumpsys package
Change-Id: I1f926af926a5eb46e9d4d8e50499d62bc8291e6b