add CarAppContextManager

- This replaces CarMessageManager and take care of
  app state sharing like active navigation or voice
  command.
- Apps can change the state and such change is
  notified to other apps.
- The informaiton is sent down to vehicle HAL as well
  to use that information for setting audio priority.
- added event count to VNS dump
- cleaned up unnecessary init/release in VNS's handler
- removed init from handler thread in car service vehicle hal:
  this just brings race when things start queickly.

bug: 25261670

(cherry picked from commit 53729bb2d3600bc23a26553f1cc3cda7d1ea0b2c)

Change-Id: I48a0215c6c8b73b5db3a2b1890febb1320096b63
17 files changed