Implement ActivityManager to LMKD reconnect functionality

In case of LMKD crashing and restarting or for testing purposes when LMKD
is killed and restarted on purpose, ActivityManager needs to reconnect and
reset the oom_adj levels so that LMKD can function. Implement a separate
LmkdConnection class handling LMKD connection and communication. We use
FileDescriptorEventListener to detect LMKD connection loss and retry logic
is implemented to reconnect and reset LMKD parameters.

Bug: 124618999
Test: kill lmkd and verify successful reconnect

Change-Id: I1b63c960aa9580cdc4f8d3697cd02fa9c18a2935
Merged-In: I1b63c960aa9580cdc4f8d3697cd02fa9c18a2935
Signed-off-by: Suren Baghdasaryan <surenb@google.com>