AVRO-3168 Enable custom coders by default

[kaliy]

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-3168
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[RyanSkraba]

Hey -- thanks so much for getting this going! I've done some tests with our internal Java code base and it looks good from our end.

I'd like to ping the dev list about this, in case anyone wants to do a test for their stuff before it appears in a release candidate -- it would be a shame to find a breakage at that point!

In any case, there's also

avro/lang/java/avro/pom.xml

Line 85 in 93ec41b

<org.apache.avro.specific.use_custom_coders>true</org.apache.avro.specific.use_custom_coders>

that should probably be adjusted -- I'm taking a look at some of the code in run-perf.sh and javadoc in SpecificData that might need adjusting, but this seems like something that should be finally turned on!