fix(parser): model PostgreSQL CREATE INDEX clauses

[minleejae]

Summary

• model key collation, operator class and parameters, sort order, and null ordering
• add structured INCLUDE, NULLS [NOT] DISTINCT, storage parameters, tablespace, and predicate fields
• update the CREATE INDEX deparser
• continue mirroring key tokens in the legacy flat parameter list for compatibility

Testing

• ./gradlew check

Fixes #2525

AI assistance

OpenAI Codex assisted with the implementation and test coverage. The changes were manually reviewed and verified against PostgreSQL syntax.

[manticore-projects]

Thank you!