Adjust right icon spacing based on font size

Split notification_2025_right_icon_margin_end into a dp-based dimension
and a sp-based one so that the spacing is still correct if the font size
changes (since the font affects the width of the expander).

Fix: 420643875
Bug: 403536710
Test: manually test notifications with and without a large icon, in all
the font and display sizes
Flag: android.app.notifications_redesign_templates

Change-Id: I70a54a6555e0f92824a3f4eb12001c755f0d710f