Define the AIDL interface for AuthGraph key exchange.

Introduce the AIDL methods for key exchange and the CDDLs for
the relevant input/output types that are CBOR encoded.

Use a standard comment format in CDDL files to indicate where additional
structure definitions can be found, in the hope that one day tooling
will be available to automatically check schema syntax.

Add authgraph to compatibility matrix

This CL merges the CLs: aosp/2750484, aosp/2750485, aosp/2750486 by
drysdale@google.com

Co-authored-by: David Drysdale <drysdale@google.com>

Bug: 284470121
Test: validate schemas with https://cddl.anweiss.tech/
Test: VtsAidlAuthGraphSessionTest (with nonsecure default impl)
Change-Id: I2793666ede028f8abe91569587c09dcac21c67e0