avro

AVRO-3531: Improve thread safety in GenericDatumReader (#1719)

* avro-3531 : make generic datum reader thread safe

* avro3531: use reentrant lock

* avro-3531: spotless modif

* AVRO-3531:use Conccurent hashmap

* AVRO-3531: reput newInstanceFromString method for backward compatibility

* Reduce visibility of the getReaderCache() method.

* Fix typo from github editor

Co-authored-by: Ryan Skraba <ryan@skraba.com>