It's the same mechanism that aconfig uses, but now it's exposed directly
to Android.bp files. (I had wanted to test it out there before making
it a property just in case it didn't work well)
Bug: 352385368
Test: go test -v -run TestJarJar.*
Change-Id: I72d797d08a250be93779ee4b038a1b8fc62123b7
