[mobile] stacked mobile icon roaming indicator

Matches the single SIM case. Also scale(-1) when RTL

Test: StackedMobileIconViewModelTest
Test: manual via demo mode
Bug: 399416492
Flag: com.android.settingslib.flags.new_status_bar_icons
Flag: com.android.systemui.status_bar_root_modernization
Change-Id: Ib274a6afc1e2e43674038efd9c64c14caf51cbe2