Add SignatureVerifier class to handle public keys from different sources am: 3bd07a5ec6 am: a7830cf9a3

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/3375769

Change-Id: I4f53cf3d6e19aa50f70b23e42aae0c79308e6616
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>