[PoC] Generate IR definitions with annotation processor

[Akirathan]

Pull Request Description

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[JaroslavTulach]

One of the issues with newly generated Java classes is the way to consume them from existing Scala passes. Preferably we do it in a way that doesn't require changes to the existing Scala code. Once I asked

"Knowing how to generate a Java class to be able to apply and unapply it would be great!"

@hubertp has provided following advice when it comes to pattern matching:

package org.enso.compiler.core.ir;

import org.enso.compiler.core.IR;
import org.enso.compiler.core.Identifier;
import scala.Option;
import scala.PartialFunction;
import scala.Tuple2$;
import scala.collection.immutable.List;

import java.util.UUID;
import java.util.function.Function;

public class Foo implements Expression {

    private final Integer a;
    private final String b;

    public Foo(Integer a, String b) {
        this.a = a;
        this.b = b;
    }

    public static scala.Option<scala.Tuple2<Integer, String>> unapply(Object x) {
        if (x instanceof Foo f) {
            return Option.apply(Tuple2$.MODULE$.apply(f.a, f.b));
        } else {
            return Option.empty();
        }
    }

and then

package org.enso.compiler.core.ir

object TestPattern {

  def testMe(x: Object): Unit = {
    x match {
      case Foo(a, b) =>
        println("A " + a + ", B " + b);
      case _ =>
        println("nope")
    }
  }

  def main(args: Array[String]): Unit = {
    testMe(new Foo(1, "foo"))
  }

}

"works just fine" according to @hubertp.