Don't pass resources to r8

R8 complains when it gets dex files in the input jar, but some tests
use dex files or dex jars as resources.  Keep resources separate
from classes until after r8 has been run.

Test: java_test.go
Test: m checkbuild
Change-Id: I1d9164d60d6b054ebb138648da07d80ee769177f