Refactor overlayable policy

To make it easier to add the actor policy in a follow up CL,
move most of the policy handling to a central location.

The strings and transformation between strings and flags is
now handled in libidmap2policies, with libandroidfw
containing the single source of policy flags.

This also extracts all the test resource IDs into an R.h
so they can be swapped without having to edit a dozen files
each time.

Bug: 130563563

Test: m aapt2_tests idmapt2_tests and run from host test output
Test: atest libandroidfw_tests

Change-Id: Ie533c9cebf938215df7586f00c38763ae467e606