Add support for literal parameters in type signatures
Support parametric types with literal parameters
Refactor AbstractType constructor to take TypeSignature
Change ModelType to extend AbstractVariableWidthType
Allow types to customize the name displayed in DESCRIBE
Remove partial support for Hive UNION type
Implement ROW type
Change Hive structs to be ROWs instead of VARCHARs
Add support for variadic type parameters
Add ROW to JSON cast
Add tests for ROW type
Implement row field accessors
Add type signature as a JSON object to StatementResource response