Move java/preprocessor to Gradle

[Stefterv]

Changes the preprocessor from the ant build-system to gradle

• Fix the Maven release script:

      FAILURE: Build failed with an exception.
            * What went wrong:
            A problem was found with the configuration of task ':java:preprocessor:sourcesJar' (type 'Jar').
              - Gradle detected a problem with the following location: '/home/runner/work/processing4/processing4/java/preprocessor/build/generated-src/antlr/main'.
                
                Reason: Task ':java:preprocessor:sourcesJar' uses this output of task ':java:preprocessor:generateGrammarSource' without declaring an explicit or implicit dependency. This can lead to incorrect results being produced, depending on what order the tasks are executed.
  

[Stefterv]

Is going to be part of the upcoming Gradle Runner