Refactor WiFi code around XL setup

Major:
- move SetupWizard-related codes to WifiSettingsForSetupWizardXL as
  much as possible
- stop using Preference for configurinig wifi network. We use
  WifiConfigUiForSetupWizardXL instead, which is base on a bare View.

Minor:
- change button handling code expecting better readability.
- hide Detail button.
- modify strings a bit.
- add logs

Bug: 3175016
Change-Id: I5b29917af73aac6a82e13ba846a9d5085f9bd523