[Wi-Fi] Create WifiNetworkDetailsFragment related version 2 files for WifiTracker2 development

Create below version 2 files for WifiTracker2 development, we can
check the feature flag only a few times and easily remove version 1
files in the future.

    src/com/android/settings/wifi/details2/
    src/com/android/settings/wifi/savedaccesspoints2/
    tests/robotests/src/com/android/settings/wifi/details2/
    tests/robotests/src/com/android/settings/wifi/savedaccesspoints2/

Bug: 143326832
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.wifi.details2
      make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.wifi.savedaccesspoints2

Change-Id: I4d2caf1ce313871605252395764b02747240f217