Move IPlatformCompat.aidl definition to framework.jar

There are non-app process usecases in framework code that need to have
access to this API.
Created a new package android.compat in frameworks/base/core following
previous definition of android.compat.Compatibility for app processes
(http://cs/android/libcore/luni/src/main/java/android/compat/Compatibility.java).

Bug: 137769727
Test: m
Change-Id: Ifc1b97ad40c2baf65a86169e101acfa72e3aae5f
Merged-In: Ifc1b97ad40c2baf65a86169e101acfa72e3aae5f