[incremental] fundamental aidl interfaces

Please review the fundamental AIDL interfaces for enabling
the Incremenetal feature. Basically there are three services:

+ android.os.incremental.IIncrementalService:
Provides basic file operation functions. Will be implemented in native.

+ android.os.incremental.IIncrementalServiceProxy:
Started by SystemServer, is it the proxy that starts native
Incremental Service. The proxy also handles Java tasks like finding
data loader service package, binding to data loader service and talking
to it. Essentially the native Incremental Service controls the
data loader service via this proxy. Will be implemented in Java.

+ android.service.incremental.IIncrementalDataLoaderService:
Defines inteface for the base data loader service. I understand that
data loader is being re-designed but I would like to get the
"placeholder" in master first, and we can iterate on the implementation
details in master.

Test: builds
Change-Id: Ifc3a43633356951b239486d66ee80d120bc4ab76