According to our docs:
https://developer.android.com/guide/topics/resources/localization.html#defaults-r-important
Some resources *require* that there is a default definition. So far,
the pain is felt when doing translations for strings that have been
renamed, etc.
This CL strips out resources that don't have a default value and define
a resource for a locale. This is conservative, but should be expanded
to other configuration properties moving forward.
Bug: 36572857
Test: make aapt2_tests
Change-Id: Ife94a1f8a2ee221f8532ffa856541a9c8c4e7143
