Reduce notif expander padding by 1dp

This gives us an additional 2dp of space between the expander and the
content text, without altering the visual aspect too much.

This change updates the paddings in:
- the standard notification expander (the dimen are used in
  notification_2025_expand_button.xml)
- the compose bundle expander
- the expander from the WIP implementation of notifs in compose

Fix: 434019277
Test: manual + screenshot tests
Flag: EXEMPT minor visual tweak
Change-Id: I741c6b1b6311fa6668a5819fb370dcaaa4568e0a