[SB Refactor] Fix WifiViewModelIconParameterizedTest.

1. Make the test data constant instead of re-creating it each time.
2. Define better toStrings for WifiNetworkModel and for the test helper
   classes.

Sample new test name:
"when INPUT(enabled=true, forceHidden=false, showWhenEnabled=false,
hasDataCaps=false, network=WifiNetwork.Active(networkId=789,
isValidated=false, level=2, ssid=null)) then EXPECTED(No internet level
2 icon)"

Fixes: 251832633
Test: WifiViewModelIconParameterizedTest
Change-Id: I31a861d0f16843ad3f46bcbe699ef4a1ce42cbc5