Mainline wifi stack module

a) Moved wifi service to a separate APK
b) Use the IWifiStackConnector to load the wifi stack from
SystemServer (similar to network stack).
c) Create a new WifiStackClient interface for system server to interact
with the wifi stack (under new services/wifi folder). Note: This not planned
to be updated via wifi-sdk Apex.
d) Add priv-app permissions for the new wifi stack APK.

Bug: 113174748
Test: Device boots up & connects to wifi networks, hotspot toggle, etc.
Test: Will send for regression tests
Change-Id: I54b3a11ed30668bad5a387370484b2bb0eabca5f
Merged-In: I54b3a11ed30668bad5a387370484b2bb0eabca5f