[java] use [javaparser] library to detect syntax errors

[sullis]

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Description of the PR

(details of the change, additional tests that have been done, reference to the issue for tracking, etc)

[wing328]

The Travis CI failure is not related to this change.

[jmini]

+1

This is an interesting change, allowing checking the validity of the code that would have been generated without having to generate it and to run maven/gradle on it.

It will not catch all cases as the compiler would to it with the compile dependencies on the classpath, but because this is earlier in the process (unit-test).

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What version of Java syntax is checked?
For example, can we leverage it to check the generated code is Java-6 compliant when the java6 option is used?
Same question with java 11 (for the moment, I do not think that the java-native client uses java-11 construct such as var introduced with java 10)

[sullis]

@jmini ready for review

[jmini]

Thank you for the this contribution!