Support validation of collection params with record types

[bentsherman]

This PR extends the support for loading a collection-type param from a CSV/JSON/YAML file to also validate and convert against a record type when used.

Notable changes:

• Add ADR for workflow params (with appendix on runtime type analysis)
• Compile params block as a hidden class to preserve runtime type information
• Validate and convert collection elements against record type when specified
• Add custom @Nullable annotation to model nullable record fields at runtime
• Extend Types helper class to render parameterized types

[netlify]

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