aconfig: create unit test targets for aconfig_protos and

aconfig_storage_file crate

also added a bunch of comments to satisfy android lint requirements

Bug: b/321077378
Test: atest aconfig.test, atest aconfig_protos.test, atest aconfig_storage_files.test
Change-Id: I9bce302ac3bc98c5347e5334d915e77337ee89c4