Evaluate expected result datatypes from json

[ckunki]

Exasol version 8 and higher provide expected data types for result set as additional JSON content.

This enables JDBC-based virtual schema adapters to

• avoid deriving the result data types from the values
• save one query

The current ticket therefore requests to evaluate the additional elements from json and transfer them into internal Pojos.

[ckunki]

How should PushDownRequest inform about whether the json actually contained an entry "selectListDataTypes" or not?

• return null or empty list?
• return an optional or a list
• have a separate method boolean hasSelectListDataTypes()

[ckunki]

Data type DECIMAL has two properties precisionand scale, reflected by method DataType.createDecimal(final int precision, final int scale).
If these properties are missing in JSON to parse PushDownRequest from: should the parser provide default value(s)? E.g. call DataType.createDecimal(-1, -1)?