Allow calling extension methods on this as receiver

[dembanakh]

Addresses #3334

Currently in Javac, whenever the call receiver is this, it is not considered as a candidate for extension method call.

lombok/src/core/lombok/javac/handlers/HandleExtensionMethod.java

Line 174 in 8bb4dc5

if ("this".equals(receiver.toString()) || "this".equals(methodName) || "super".equals(methodName)) return;

This PR makes the behaviour consistent with that of Eclipse's handler, I believe. In other words, explicit this call would be considered as a possible extension method call.

[dembanakh]

@Rawi01 Could you take a look at this by any chance? 😃

[Rawi01]

• Please add your name to the AUTHORS file
• It would be great if you can rebase this branch on the current master. We recently enabled GitHub Actions to run the whole test suite and that way we do not have to run the tests locally. (Some eclipse test will fail but you can ignore that)

I'm not sure if extension methods should ever work like that but it should at least be consistent. It feels a little bit weird because you could simply add the method to your class instead of using extension method at all.

[dembanakh]

Thanks, I fixed the failing test and rebased.

4 test suites are failing (the same 4 that fail on master), but the others pass successfully, so I hope that's alright.

While it indeed feels strange to call an extension method on this, I think this option is worth keeping. Consider e.g. the case where you have to use the extension method both inside and outside the receiver's class

@ExtensionMethod(Extensions.class)
class A {
  public void reset() {
    this.clear();
    // ...
  }
}

@ExtensionMethod(Extensions.class) 
class B {
  private A a;

  public void run() {
    a.clear();
    // ...
  }
}

class Extensions {
  public static void clear(A a) {}
}

[Rawi01]

In your example you could also add the clear method to A but this still might be useful if the base class is a third party/framework class.