Flink: Using RowData to avro reader and writer

[JingsongLi]

There was problems with the previous row conversion. For example, array type should be T[] instead List.
According to discussion from #1215 , We can try to only work with RowData, and have conversions between RowData and Row.

The works can be:

• Extract ValueReaders.decimalBytesReader for reusing code. avro: Extract ValueReaders.decimalBytesReader #1233
• Extract DecoderResolver to provide cached ResolvingDecoder for resolving avro decoder. avro: Extract DecoderResolver to provide cached ResolvingDecoder for resolving avro decoder #1234
• Abstract AvroWithPartnerSchemaVisitor to extract specific avro logical from AvroSchemaWithTypeVisitor and AvroWithSparkSchemaVisitor. avro: Abstract AvroWithPartnerSchemaVisitor #1235
• Implements FlinkValueReaders and FlinkValueWriters and refactor FlinkAvroReader and FlinkAvroWriter. Flink: Using RowData to avro reader and writer #1232

[JingsongLi]

CC: @rdblue @openinx @chenjunjiedada

[rdblue]

Thank you for the pull requests! I'll try to get them reviewed this weekend. Sorry that I'm running a bit behind with reviews right now.