Improve handling of java files in repl

[jneira]

Follow up of #805 (fixed with #905)

Although the repl is able to load java object files the handling could be improved:

• Allow reload of .java, .class and .jar files
  • Actually .java and .class are compiled in a auto generated __extra.jar
  • The jar files are being locked by eta (it should be unlocked after create and use it) and cant be changed
  • But likely the eta-serv classloader will not see the updated jars
  • The solution could be load directly the classes contained in those jars to use class reloading of eta-serv
    • Although it could be expensive for big jars
• Load the classes of java files informed in params (i.e. the files listed in cabal java-sources) when initialize the dynamic linker: https://github.com/typelead/eta/blob/master/compiler/Eta/REPL/Linker.hs#L150-L172
  • It already loads the package jars
  • Avoid loading them in the first load but dont remove the feature of :load path/to/my.jar on the fly
• In general, as rahulmut suggested in #805, try to not load java files that have not changed since last load.

[jneira]

The solution could be load directly the classes contained in those jars to use class reloading of eta-serv

i guess we should read the classes from jar and use from Eta.REPL

loadClasses :: HscEnv -> [(String, String, ByteString)] -> IO ()

It needs the class name, the class info and the actual contents.

@rahulmutt i see that Eta.Utils.JARhas methods to read entries, but is there some existing way to read classes from? Getting [(String, String, ByteString)]or ClassFile