Populate hidden API dark greylist

This patch will iterate over all classes in the light greylist and
add the remaining (currently blacklisted) class members into the
dark greylist. This is meant to mitigate the impact of the feature
on legacy apps, in case their hidden API uses have not been detected
by our analyses. The dark greylist entries will be available to apps
targeting pre-P SDK versions, but blocked for apps targeting P or later.

Bug: 64382372
Test: make out/target/common/obj/PACKAGING/hiddenapi-dark-greylist.txt
Change-Id: Id1ef4ab523b3b4d1333b5fbf2b3e6622ef2be607