Wi-Fi DPP code refine

1. call Activity#setResult only for RESULT_OK case
2. refine @VisibleForTesting usage
     remove redundant assignment otherwise = PRIVATE
     set all @VisibleForTesting annotated methods package scope
3. rename WifiQrCode#SECURITY_WPA to WifiQrCode#SECURITY_WPA_PSK

Bug: 120645817
Test: atest WifiQrCodeTest
      atest WifiDppConfiguratorActivityTest
      atest WifiDppEnrolleeActivityTest
      atest WifiDppQrCodeGeneratorFragmentTest
      atest WifiDppQrCodeScannerFragmentTest
      atest WifiNetworkListFragmentTest
      atest WifiDppChooseSavedWifiNetworkFragmentTest

Change-Id: Id5de7eadc73185716422fc0d197f82bdd025ce45