fix: support FILTER after ordered-set aggregates

[minleejae]

Valid PostgreSQL expressions such as percentile_cont(0.5) WITHIN GROUP (ORDER BY score) FILTER (WHERE active) currently fail to parse. Accept FILTER after WITHIN GROUP and render it in that position in both AST and visitor output, while preserving ordinary aggregate/window FILTER behavior.

Reuse AnalyticExpression and share filter parsing/rendering helpers. In the PostgreSQL dialect, reject the reversed FILTER-before-WITHIN-GROUP form. Tests cover ordered-set and hypothetical-set aggregates, filter/order expression visitors, malformed predicates, and window regressions.

Syntax reference: PostgreSQL aggregate expressions.

Validation:

• Java 17 Gradle check: 7,820 XML-reported tests, 0 failures/errors, 25 skipped; formatting, grammar ambiguity, Checkstyle, PMD, and JMH compilation passed. Formatting was checked against upstream/master using a local Spotless ratchet override.
• Actual PostgreSQL 17.11 server: 8 accepted and 5 rejected SQL cases matched the expected behavior.
• Executed both AST and StatementDeParser output for the accepted cases on the same server: 16 successful executions.

[manticore-projects]

Thank you!