User WifiPickerTracker API for saved network preference text

Change the source of the saved network preference text from WifiManager
to WifiPickerTracker and update it through the
WifiPickerTrackerCallback.

Bug: 70983952
Test: atest WifiSettings2Test
Change-Id: Ia0a61f174a061892cd9376c16402e4983eaaa03c
2 files changed