[Notif redesign] Circular icons for Messaging Notifs

Note that:
- notification_2025_template_conversation is forked from notification_template_material_conversation.
- notification_2025_messaging_group is forked from notification_template_messaging_group.
- notification_2025_conversation_icon_container is forked from notification_template_conversation_icon_container.
- notification_2025_conversation_face_pile_layout is forked from conversation_face_pile_layout.
- notification_2025_hybrid_conversation is forked from hybrid_conversation_notification.

Bug: 378660052
Test: visual test, screenshot tests to come later
Flag: android.app.notifications_redesign_templates
Change-Id: I9381c1fe4f35e39fc508bba971fbeb2b63fd0def