[Notif redesign] Update notification importance preferences

Turns out there was even more duplications of these guts buttons than we
thought - they also appear in channel settings and for priority
conversations. This makes those views also match the new design from the
guts.

Note that notification_2025_importance_preference.xml and
notification_2025_priority_conversation_preference.xml are forks of
notif_importance_preference.xml and
notif_priority_conversation_preference.xml respectively.

Bug: 394822197
Fix: 409366749
Flag: android.app.notifications_redesign_templates
Flag: android.app.notifications_redesign_fonts
Test: manual
Change-Id: I517a731580e3be1578d6fe9679a98505c3c84839