[Sb refactor] Add WifiIcon.fromModel for use in QS

This function is a simple mapping from a WifiNetworkModel to a WifiIcon.
Since we want a WifiIcon object to represent a WifiNetworkModel in
exactly the same way in QS as in the status bar, moving this function
allows us to reuse it later

Test: tests in statusbar/pipeline
Bug: 291321279
Change-Id: I2fae11827c6cfd07d08fccc3eb5351883b706f90