MSSQL: Add support for OUTPUT clause on INSERT/UPDATE/DELETE

[guan404ming]

Why

MSSQL's OUTPUT clause allows returning inserted/deleted column values from DML statements, but was only supported on MERGE.

How

• Add output: Option to Insert, Delete, and Update AST structs with correct mid-statement positioning
• Reserve OUTPUT and VALUES keywords for table/column alias contexts to prevent ambiguous parsing
• Add tests covering OUTPUT with and without INTO on all three statement types

[iffyio]

for these comments, could we include the link to the mssql docs describing the syntax? it would help with nagivation when folks look at the struct

[iffyio]

Suggested change

	// MSSQL OUTPUT clause appears after FROM table, before USING/WHERE
	// https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql

[iffyio]

Suggested change

	// MSSQL OUTPUT clause appears between columns and source
	// https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql

[iffyio]

Suggested change

	// MSSQL OUTPUT clause appears after SET, before FROM/WHERE
	// https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql

maybe we can introduce a helper function maybe_parse_output_clause() that can be called from the relevant statement parsing functions?

[iffyio]

Suggested change

	// MSSQL OUTPUT clause on INSERT/UPDATE/DELETE
	// https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql