[WifiNetworkSelector] Inject Candidate Scorer

Instantiate and register Candidate Scorer in WifiInjector instead of
in the constructor of WifiNetworkSelector in order to simplify unit
testing.

Bug: 124023173
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Change-Id: I92c752763a9adf933a41adcc5d97440c9ff7d7a3
3 files changed