AAPT2: Disambiguate merging of resources

Merging local app resources is slightly different than merging
resources from a static library.

Local app resources may not have a package name set, but we do take interest in the
ID set for the package (should be 0x0 or match the ID of the app we're building).

Static library resources have an explicit package name defined for them, so we
only merge resources from that package.

Change-Id: I95e559ae94cc1df6972e77a347b1b37a93674c4d