Allow using reserved package IDs

Pre-O, the platform treats negative resource IDs [those with
a package ID of 0x80 or higher] as invalid.  In order to work
around this limitation, we allow the use of traditionally
reserved resource IDs [those between 0x02 and 0x7E].

Bug: 78041707
Test: ./out/host/linux-x86/nativetest64/aapt2_tests/aapt2_tests
Test: ./out/host/linux-x86/nativetest/libandroidfw_tests/libandroidfw_tests
Test: Manual. Create a feature split with a package ID of 0x7E and see it runs and can reference base resources.

Change-Id: I3d9782cc05d3a55e1a2467bf39566788847e1160