hiddenapi: Print warnings for @CorePlatformApi violations

When accessing a method/field at runtime, determine the context of both
the caller and the callee, and add new logic for the case
"platform -> core-platform" which used to be always allowed.

If the callee is marked with kAccCorePlatformApi, access is allowed.
If not, a warning is printed into logcat.

Bug: 119068555
Test: 674-hiddenapi
Change-Id: I64839596bf6eb06d7a169fd59b18fd82c140ce6e