Support GraalVM and alternative runtimes in Debian packages
1. KSC requires `java8-runtime-headless` . There are other OpenJDK JRE runtimes. They should be marked as alternatives.
2. GraalVM has no packages for Debian for now, so I propose to remove https://github.com/kaitai-io/kaitai_struct_compiler/blob/master/build.sbt#L131 in order not to force installation of an unneeded package.
3. GraalVM allows ahead-of-time compilation. It may make sense to apply it on KSC and use the precompiled compiler from the shell script.