PARQUET-1496: Update Scala to 2.12

[Fokko]

Make sure you have checked all steps below. Updated the tests a bit as well. There were some conflicts between both test.thrift files. I've consolidated them to avoid issues.

Updating to Scala 2.12 is required to support Java 11.

Jira

• My PR addresses the following Parquet Jira issues and references them in the PR title. For example, "PARQUET-1234: My Parquet PR"
  • https://issues.apache.org/jira/browse/PARQUET-XXX
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

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

[nandorKollar]

This file has only style changes, would you mind reverting it?

[Fokko]

Valid point, done!

[Fokko]

I've reverted a couple more unrelated changes.

[Fokko]

Does someone have some spare time to review this? Would be great to move Java 11 support forward.

[Fokko]

@nandorKollar Are you fine with the current PR as is? 👍

[nandorKollar]

Sure, thanks @Fokko!