hiddenapi: Split stubs into public/system/test classpaths

The hiddenapi tool needs to build a class hierarchy from API stubs.
These are inconsistent between public, system and test API stubs.
This patch splits stubs into the three corresponding categories
and groups the JARs being passed to hiddenapi.

Test: m appcompat
Bug: 76424618
Change-Id: I3f707070d44f04578bc6148a45f2283bcf060703