AVRO-2468: Fix broken data interoperability on the Perl bindings

[sekikn]

• Fix Avro::Schema to take namespace into consideration
  when parsing named types in arrays/maps/unions.

• Fix Avro::Schema to encode fixed type's size value
  into numeric when it outputs Avro schema.

• To ensure the above fixes work, add data interop test
  for the Perl bindings.

Make sure you have checked all steps below.

Jira

• My PR addresses the following Avro Jira issues and references them in the PR title. For example, "AVRO-1234: My Avro PR"
  • https://issues.apache.org/jira/browse/AVRO-2468
  • 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:

I added the following tests:

• xt/interop.t: test for ensuring data interoperability between other languages.
• xt/schema.t: test for ensuring the revised parser can parse named types in arrays/maps/unions correctly. It tries to parse all schemas under the toplevel "share" directory, so it fails right now because of AVRO-2466. But once it's merged, this test is supposed to succeed.

I put these tests under the xt directory as "author tests", since they depends on the contents under the toplevel "share" directory, which are not included in the release distribution of the Perl bindings.

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

[sekikn]

Resolved conflicts.