Merges partiql-lang-kotlin generator into PIG as 1.x

[rchowell]

Description of changes:

PartiQL Lang Kotlin is migrating to an updated version of PIG that is now stable. The new README contains details regarding the differences.

https://github.com/partiql/partiql-ir-generator/blob/lorax/README.adoc

Notably though, permuted domains have been dropped. To maintain an option for existing customers, all 0.x behavior is preserved under a legacy subcommand. The only other change is that the runtime library has been repackaged to org.partiql.pig.legacy.runtime as 1.x does not require a runtime library.

PIG 1.x set out to address PIG feature requests by introducing an updated modeling language and generator which enable features such as:

Modeling Additions

• List, Map, and Set Types
  • Support modeling variadic maps and/or sets #70
  • Model Variadic Elements with an Ion List #76
  • Support Defining Type of A List of Nullable Int #134
• Int, Float, Double, Bytes, String types
  • Support string type #122
• Enum Types
  • Add type enums #14
• Imported Types
  • Support for timestamp type #51
  • Support BigInteger for int types #46
• Sum type definition as the variant of a sum type
  • Consider adding union types as an alternative or replacement for sum types #78
• Inline type definitions
• Scoped type definitions
• Scoped type names

Kotlin Specific Features

• No runtime library
• Primitives nodes are optional
  • Justify the existence of LongPrimitive, SymbolPrimitive and BoolPrimitive in their kdoc #79
• Explicit library mode
  • Enable explicit library mode #64
• Visitors use conventional style
  • Parameterized return type in generated visitors #123
  • Make visitors able to visit any domain type #66
• Nodes have a children construct, enabling recursion without a visitor.
• Dynamic code generation via poems rather than templating.
• Generated DSL now uses "type-safe" builders rather than just factory methods
• Generated DSL allows for a custom factory
• Jackson databind integration for serializing a tree to arbitrary Jackson formats
  • Custom JSON serialization with Ion-Jackson possible, for interop with languages that don't have Ion SDK's? #119

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.