[SB Refactor] Supprt activity in/out for carrier merged connections.

Bug: 238425913
Bug: 264684296
Test: manual: `adb shell am broadcast -a com.android.systemui.demo
-e command network -e wifi carriermerged -e level 2 -e activity out` ->
shows carrier merged connection with activity arrows
Test: atest CarrierMergedConnectionRepositoryTest

Change-Id: If3e00d82c0278bba68da08f972da002729f1a5a3