[Notif redesign] Bigger "small" icon in collapsed notif

Increase the size of the "small" icon (and corresponding margins) for
collapsed notifications.

Note that notification_2025_template_collapsed_base is a fork of
notification_template_material_base.

Bug: 378660052
Test: visual test, screenshot tests to come later
Flag: android.app.notifications_redesign_templates
Change-Id: If24e539a311a9567607c053f11817dfb88100f84