Refine Wi-Fi DPP fragments.

1. WifiDppQrCodeBaseFragment only declairs common UI components between fragments.
2. Initiate UI components in onViewCreated of each View.
3. Remove the only one usage of @NonNull since it should be used consistently
   throughout the class if we want to use it.
4. Use android.R.id for icon/title/summary

Bug: 120645817
Test: atest WifiDppConfiguratorActivityTest
      atest WifiDppEnrolleeActivityTest
      atest WifiDppQrCodeGeneratorFragmentTest
      atest WifiDppQrCodeScannerFragmentTest

Change-Id: I54f99a3072533cec46f0e47753ee0331fecf2ada