AVRO-3156: SpecificRecordBuilder performance degradation

[steven-aerts]

The change introduced in spark 1.9.0 which changed:

SpecificData.get()

into:

SpecificData.getForSchema(schema)

introduced a significant performance degradation in environments where the class belonging to the schema is provided by a different classloader then the classloader containing SpecificData.

In this patch we use the classCache of the default SpecificData so the sometimes expensive classloader codepath is cached.

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-3156

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[steven-aerts]

Fixed by AVRO-3186 in #1304