Ref scala/scala-dev#912

Problem

#8018 / #8604 implemented forked Scala REPL console (🎉 ). One area of improvement is that ConsoleMain brings in the entire Zinc into the classpath, which includes JLine. Apparently this still pins Scala compilers to use the same version of JLine as sbt.

Expectation

If we could implement a lighter weight ConsoleMain, perhaps using Java 8 + "Scala instance" (Scala REPL or compiler JARs, compiler bridge, compiler interface) and glue code without JLine, we might be able to free Scala compilers from this constraint.