Refactor TypeInstrumentation#transformers() method

[mateuszrzeszutek]

This PR was inspired by DataDog's AdviceTransformation interface introduced in DataDog/dd-trace-java#2673 (FYI @tylerbenson)

I've changed the TypeInstrumentation interface and introduced TypeTransformer:

interface TypeInstrumentation {
  // ...

  // removed the map-returning transformers()
  void transform(TypeTransformer transformer);
}

interface TypeTransformer {

  void applyAdviceToMethod(
      ElementMatcher<? super MethodDescription> methodMatcher, String adviceClassName);

  void applyTransformer(AgentBuilder.Transformer transformer);
}

This has several merits:

• we no longer need to create those transformer maps (which I believe was the main reason for the DD change);
• this allows us to introduce type transformations other than advices - e.g. adding the static initializer (see How to instrument static initializers? #2685)

The PR is has lots of changed files, but 98% of it is just changing all existing TypeInstrumentations. The most interesting parts are in javaagent-extension-api and javaagent-tooling.

[laurit]

If TypeTransformer had applyAdviceToMethod that takes class instead of className we could build a byte buddy plugin similar to MuzzleCodeGenerationPlugin that translates from class to className and calls the string version of applyAdviceToMethod.

[tylerbenson]

I would suggest splitting this into at least two commits to make it easier to review. (one with the API change, another with all the instrumentation changes)

[mateuszrzeszutek]

I would suggest splitting this into at least two commits to make it easier to review.

That's a good idea, done. The first commit in this PR contains all the API changes, the second one is just changing all TypeInstrumentations in the project.

[tylerbenson]

Much better.

[trask]

I will not miss this method signature 😂

[anuraaga]

Awesome!