Javaparser

Java parser for dotty.

As we discussed, three tests are still failing:
* t2409:
  Requires import of companion object before first constructor.
* t1751 and t294:
  Tree transformer does not transform repeated method arguments within an annotation instantiation.

Review by @odersky @DarkDimius


There is an abstract class TokensCommon that contains all of the tokens that are common to Scala and Java (with the Scala-only ones commented out).

Then object Tokens extends TokensCommon with the Scala-only tokens.

Similarly, JavaTokens extends TokensCommon with the Java-only tokens.

This is the same design as in scalac.