avro

AVRO-3001 AVRO-3274 AVRO-3568 AVRO-3613: Add JSON encoder/decoder for C# (#1833)

* AVRO-3001 AVRO-3274: Add JSON encoder/decoder for C#

* Add more comments for public/protected members

* Make CodeQL happy

* Make CodeQL happy again

* Minor optimization

* Fix cosmetic issues

* Fix JsonEncoder.StartItem accessibility

* Minor doc fix

* Add fixes and test for JSON encoding/decoding logical types

* Fix fullname calculation for logical schemas

* Fix for AVRO-3613

* Fix for AVRO-3568

* Add union with record test

* Fix test

* Incorporate review feedback

* Incorporate review feedback

* More cleanup

* Revert previous cleanup in favor of recommended cleanup

* Incorporate more review feedback

* Incorporate latest review feedback

* Add more unit tests

* Simplify string constant

* Simplify string constant

* Simplify string constant

* Simplify string constant

Co-authored-by: Martin Grigorov <martin-g@users.noreply.github.com>