Adds D8Compiler, which applies to the Android Java and Android Kotlin
languages. D8Compiler instantiates a JavaCompiler or KotlinCompiler
using the java/kotlin dependencies' paths for D8 in the infra repo.
compiler-finder.ts has been updated to allow for duplicate compiler IDs
for 'android-java' and 'android-kotlin', as it is expected that the
compilers used for these languages is the same.
