Explicitly collect on mobile subscriptions in MobuileUiAdapter

The adapter was previously using an `onEach` to trigger the callback to
`StatusBarIconController#setNewMobileIconSubIds`, which is a side-effect
of the flow rather than being explicit.

This CL makes it so `MobileUiAdapter` explicitly launches a `collect`
job on the subscription list, making it clear that it is setting the new
subscription list on the icon controller.

Test: tests/src/com/android/systemui/statusbar/pipeline/mobile/*
Bug: 249790009
Change-Id: I0fdcc086c1028ac5f3e50942b4bd3a9dfdb9871f