Structure SQL Server routine operations and table return types

[minleejae]

Fixes #1978. Fixes #715.

Under Dialect.SQLSERVER, CREATE, ALTER and CREATE OR ALTER FUNCTION/PROCEDURE share one declaration path. CreateFunctionalStatement.getOperation() exposes the operation, and FunctionReturnType structures scalar returns, inline RETURNS TABLE, and named return tables with ordered columns and constraints. Return tables reuse existing TableElement models, traversal and deparsing, so AST edits and custom expression visitors affect emitted SQL.

The reported function and procedure examples are covered. Function capture balances nested blocks and CASE expressions without consuming the next statement. Procedure definitions preserve their entire batch, including statements after END, transactions and TRY/CATCH. Parse procedures one batch at a time; client-side GO splitting is not added. Parameters, options and bodies remain token lists, and other dialects retain the existing representation. Table discovery still rejects opaque routine bodies.

Validation: full Gradle check and Maven verify, including operation capability checks, table constraints, AST mutation, visitor context, custom deparsing, script boundaries, original examples and existing function/procedure regressions.

References: CREATE FUNCTION, CREATE PROCEDURE.

[manticore-projects]

Thank you!