[Notif redesign] Bigger "small" icon in old messaging notif

Note that notification_2025_template_collapsed_messaging is a
fork of notification_template_material_messaging.

There's a KI where the second line in the collapsed notification is aligned poorly, but it will be fixed in a follow-up CL.

Bug: 378660052
Test: visual test, screenshot tests to come later
Flag: android.app.notifications_redesign_templates
Change-Id: Ic603d0b12afa6082be1313f2d1c8960319fb9e26