[SB][Notif] Add a bit of extra side padding to the chips.

Also replaces the spacing between chips and other status bar components
to use a resource.

Fixes: 393371967
Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips
Test: Verify chips have just a bit of extra spacing (see
b/393371967#comment3)

Change-Id: I39b6fe2c018a1cd7486931756799f1446997a24b