Adding xef.java module

[Yawolf]

The idea is to have this in Java:

class Person {
  public String name;
  public Int age;
}

try(AIScope scope = AIScope(...)) {
  Person person = scope.prompt("Give me a person", Person.class, ...)
  ...
}

AIScope from xef-core has been renamed to CoreAIScope for avoiding name collisions in Java and because it's a piece, from core project, needed for creating/instantiating specific AIScope in other implementations. BaseAIScope could work too.

CoreAIScope is now an AutoCloseable object so it can be used with a try-with-resources form Java.

• Adding a new module for Java implementation
• prompt compiles and is working
• promptMessage compiles and is working
• image compiles and is working
• pdf compiles and is working
• contextScope compiles and is working

[nomisRev]

This PR is now ready for review, and ready to be merged. We want to prevent this PR from growing too large, and we need to investigate what we want to do with PDF, etc in terms of architecture.

When this is merged we can start porting more Java examples.

[diesalbla]

Couple suggestions...

[raulraja]

Looks great @nomisRev @Yawolf !