Add class for holding information about calling app

This CallingAppInfo class contains calling app package and app
signature. Since Credential manager pings multiple providers, this
is a performance optimization so that each provider does not need to
query app signatures separately.

Test: Built & deployed locally
Bug: 253155222
API-Coverage-Bug: 247549381

Change-Id: Iec580a252c4f27b92d02fe5c50e1085ee23f8f4b