contexthubhal: add nanohub contexthub impl and service

For now, maintain legacy context_hub.default.so support.

Bug: 70933028
Test: verify messages still successfully passed back to contexthub service
Change-Id: I9a36b4f6d581243b9de3a5e6d742d17c1aa49f88
Signed-off-by: Ben Fennema <fennema@google.com>