Use SettingsLib expressive flag when using custom adapter in SUW.

The custom adapter is trying to temporarily fix an issue coming from the
SettingsLib's PreferenceGroupAdatper using a themed attribute, so it
should be flagged with the SettingsLib expressive flag.

Bug: 410060930
Test: manually with OEM expressive flag on and SettingsLib flag off
Flag: com.android.settingslib.widget.theme.flags.is_expressive_design_enabled
Change-Id: I675ece06f1f02b5156dbc2fd247f93801426ab15