Pulsar support for Apache Avro library as published by Apache

**Is your enhancement request related to a problem? Please describe.**

We have a requirement to use both Kafka and Pulsar with Apache Avro Schemas. This is not possible currently as Pulsar uses it's own shaded (masked) version of apache avro implementation, which looks identical to Apache Avro.

**Describe the solution you'd like**

The enhancement is for Pulsar to work directly with Apache's Avro implementation.

**Describe alternatives you've considered**

Currently we are defining Schema's using Apache Avro Generic Record and then writing conversions to work with Pulsar's shaded version.

**Additional context**

Add any other context or screenshots about the feature request here.

We have written converters to allow schemas which serialize to `org.apache.avro.generic.GenericRecord` to allow serialization to
`org.apache.pulsar.shade.org.apache.avro.generic.GenericRecord`.

The issue names no repository files, tests, or entry points. Start by tracing Pulsar’s shaded Avro schema and serialization integration, then compare it with the Apache Avro GenericRecord converters described in the report. Done means Pulsar can work directly with Apache’s Avro implementation without conversion to the shaded type, with Kafka and Pulsar schemas remaining usable.

Written by the indexing model from the issue text.