Address known limitations of MULTISET support

[lukaseder]

jOOQ 3.15 introduced support for nested collection emulations via JSON/XML: #3884

Many issues were addressed in 3.16: #12021

This issue addresses remaining known limitations of the 3.16 implementation, including:

Bugs

• Records detached when converting nested multiset #12269
• ExecuteListener lifecycle events aren't triggered within MULTISET #12575
• Standard SQL MULTISET emulation using XML produces a null Result #13080
• Cannot use H2 enum values in JSON documents #13081
• SQL Server MULTISET as JSON emulation of empty subquery produces NULL instead of empty Result #13082
• MULTISET and ROW generated nested records should not have their changed flags set to true #13403

Limitations, missing features

• The behaviour of a MULTISET with duplicate column names is currently undefined
  • We also don't have any unit / integration tests that validate duplicate column names in fetchFromJSON(), and fetchFromXML(). It should be possible in both, but the former probably "swallows" one of the duplicates because our parser is using java.util.Map
• Support for custom data types, including the built-in ones, such as hstore, inet, etc.
  • Things already work with converters
  • How can we get things to work with bindings?: Bindings won't be supported, it's not possible

To be continued: #13589

[lukaseder]

Work will be continued in jOOQ 3.18: #13589