Make UiccAccessRule certificate utils accessible.

UiccAccessRule includes functionality for getting Signatures from a
PackageInfo and hashing a cert. Instead of duplicating this code in
CarrierPrivilegesTracker, make it visible with @hide.

Bug: 147391402
Test: atest FrameworksTelephonyTests
Change-Id: I4f95ab512e94cd851a6928d8eb7918d5a04bfa60