Create Helper Classes for WifiTrackerLib

- Create a WifiTrackerBase for the base worker thread

- Create a SavedWifiHelper for the saved Wi-Fi network tracker

Bug: 258542666
Test: manual test
atest -c WifiTrackerBaseTest \
         SavedWifiHelperTest

Change-Id: Ie6b2f5b348367376da96737acdf5b8e65ecaf067
4 files changed