[Java] SpecificData.getClassName must replace reserved words

[Java] SpecificData.getClassName must replace reserved words

When makes Java Class, SpecificCompiler adds "$" after reserved words like public, new, etc...

https://github.com/apache/avro/blob/master/lang/java/compiler/src/main/java/org/apache/avro/compiler/specific/SpecificCompiler.java#L1129

https://github.com/apache/avro/blob/master/lang/java/compiler/src/main/java/org/apache/avro/compiler/specific/SpecificCompiler.java#L643

For example, if the namespace of a schema is db.public.table, then the package name of the generated Java Class, made by SpecificCompiler, is db.public$.table. (Because public is a reserved word in java)

But when deserializes an Avro Record to a SpecificRecord, SpecificData.getClassName returns db.public.table.Name.

So, it can't find a class by name from SpecificData.getClassName.