Expose WifiInfo & NetworkSelectionStatus Builders for SettingsUnitTests

SettingsUnitTests needs to set up WifiInfo &
NetworkSelectionStatus objects in a specific state
and parcel/unparcel them. Create @SystemApi
Builder classes in order to allow
SettingsUnitTests to create these objects while
maintaining the immutability of their APIs.

Bug: 138801922
Test: atest SettingsUnitTests
Change-Id: I40034d08396efc45bd24e16bd788e702366d5dd2