[Catalyst] Refine Wi-Fi preferences

- Use application context to get system services to avoid memory leaks

NO_IFTTT=Catalyst only

Bug: 385116691
Flag: EXEMPT bugfix
Test: Manual testing
atest -c WifiHotspotSwitchPreferenceTest \
         WifiSwitchPreferenceTest

Change-Id: I4340136d8d0118801ef450809424127f84afbb92