Adding automatic heap dumping for system server.

This adds a request to ActivityManager to track the system server's pss heap
and make sure it doesn't go above a predefined limit. If it does, the dump is
generated and a notification is posted.

Bug: 77490269
Test: flash device and test with 100MB and 150MB limits
Change-Id: Ie886cc36860e8557fbd037b3bfd4975d12806a4b