Add a hidden API to detect ravenwood environment

We should minimize uses of it, but once in a while,
it's useful as a last resort.

Bug: 340556010
Test: atest FrameworksCoreTestsRavenwood:com.android.internal.ravenwood.RavenwoodEnvironmentTest
Test: tree hugger for device side tests
Merged-In: Ice651a55cad092514466dd56940a2cf7b2285e4e
Change-Id: Ice651a55cad092514466dd56940a2cf7b2285e4e