Handle multiple packages of same name in 'aapt2 convert'

aapt2 currently looks-up packages only by package name and then verifies
whether the package ID has the expected value. For pre-L we need to be able
to handle resource tables having packages of same package name but
different IDs.

Note that this CL fixes only proto->binary conversion but many other aapt2
commands are still affected. This is because many transformations still
consider package name as sufficient identifier of a package.

Bug: 72143207
Test: Manual
Change-Id: Id8a920d6cd15bec747d3124270f5bcb7f48924cf