Automatically greylist code in 3P packages

generate_hidden_api_lists now receives a file containing package names
which need to be greylisted (although it could be made to work with any
api list required).
Also took the opportunity to clean up the tests to reflect the more
strict code.

Bug: 129387816
Test: m appcompat
Test: frameworks/base/tools/hiddenapi/generate_hiddenapi_lists_test.py
Change-Id: I619f8581d166aa48eda572bc0053d8739d6420eb