Fix numerous issues with DdmVmInternal allocation tracking

Issues addressed:
- Using without JDWP attached caused native crash.
- When buffer is full (64k entries), number of entries reported was 0.
- Disabling tracking after disabling tracking caused native crash.
- Asking for allocations after disabled caused native crash.
- Lock ordering issues between mutator lock and alloc tracker lock.

Adding 098-ddmc test to cover these cases.

Bug: 17392248
Change-Id: I45c0abbfb3dd7a7421aea3bbba2ea8d05225e48b