[SB Refactor] Expose the wifi repository flows as StateFlows.

From Evan's comment on ag/19745297, we should expose our flows as
StateFlows so that it's clear to callers that it is a hot flow, not a
cold flow.

Bug: 238425913
Test: statusbar.pipeline tests
Test: manual: Verified wifi icon via new pipeline still works
Change-Id: Icec5c30f203bd11ade72f11b8fbb2b296394a693