Recoder must be removed

[wadoon]

The Recoder framework is out-of-date and need to be replaced.

The solutions:

1. Use a Java compiler (Eclipse, etc..) and exploit the compiler to generate a proper AST. Name resolution for JML&Co needs to be done by down-compilation to Java. The same goes for extra KeY-Java constructs like method frames, loop scopes, ...
   The Eclipse compiler comes in a simple distributable form. But the Javac compiler could be accessed via the Tool API when a JDK is used with limited information.

2. Extending Recoder: Adapt Recoder to new Java constructs.

3. Switch to the JavaParser project.

We did (3) in #3120. The code lies here https://github.com/wadoon/key-javaparser.