service: Added RemoteCallbackMap

Added the RemoteCallbackMap template class which allows storing
IInterface subclasses in an associative array while tracking the
death of the remote process that owns the associated binder. This is
similar to RemoteCallbackList but stores entries in key-value pairs.

Also fixed some RemoteCallbackList documentation and change the code to
use std::unordered_map rather than std::map.

Bug: 23793954
Change-Id: I205c0491d21fef3bc5eeb5c4a7356dab4b6eb8dc
3 files changed