AVRO-2838: Conditional Java String type schema modification

[slominskir]

Add option to skip the schema mangling step in the Java AVRO compiler that breaks compatibility between Java and Python (and other languages).

Make sure you have checked all steps below.

Jira

• My PR addresses the following issues:
  • https://issues.apache.org/jira/browse/AVRO-2838

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  • org.apache.avro.compiler.specific.TestSpecificCompiler.java#testSettingDoNotModifySchema

Commits

• My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain Javadoc that explain what it does

[slominskir]

Ran "mvn spotless:apply" to correct formatting then force pushed (squashed changes to keep single commit with required message prefix)