[Sb refactor] Support NOT_DEFAULT_DATA network type

In the old pipeline (and now here), we track the default data
subscription id, and any mobile network which is NOT that subscription
(i.e., every non-default) gets a specific network icon group (per
MobileMappings) which encodes a null RAT icon and a proper content
description.

This CL builds upon the revert and uses the default data subId to
implement this icon group.

Test: MobileIconInteractorTest
Bug: 264683083
Bug: 238425913
Change-Id: I06365d1923714f7855ea4b179bd4bdc20d9d54ba