hiddenapi: Support 'core-platform-api' flag

Libcore class members annotated with @CorePlatformApi now generate
a new hiddenapi flag. This is the first of "domain API" flags which
can be used in conjunction with API list flags. Therefore modify
the 'generate_hiddenapi_lists.py' logic to treat them differently.
Specifically, the script marks otherwise unassigned class members
blacklisted. A class member with 'core-platform-api' may still not
be assigned an API list and should be blacklisted.

Bug: 119068555
Test: m appcompat
Change-Id: I2b67e7a619677e853c87bc2da934410458ce4d14