feat(grammar): SET configuration_parameter in CREATE FUNCTION and PROCEDURE

[sebsnyk]

Problem

CREATE FUNCTION ... SET search_path = public, pg_temp AS $$ ... $$ does not parse; #364 reports it. Any function that pins search_path (most SECURITY DEFINER functions, and every function in pg_partman) fails at the SET.

Solution

A function_set option: SET name { TO | = } value [, value ...], with DEFAULT, ON and OFF as values like set_statement, plus SET name FROM CURRENT. It joins the other options on create_function and create_procedure, so it is accepted before or after the body in any order.

create_function and create_procedure are now prec.right. Without it a trailing SET inside a T-SQL WHILE cond BEGIN ... END body, where statements have no terminating semicolon, could also be read as the next statement; right associativity keeps it with the definition, which is the PostgreSQL reading.

Notes

• tree-sitter test: 511 corpus tests on main, 513 with this PR (one each in functions.txt and procedures.txt), plus the 2 highlight tests. scripts/test-keywords.sh passes; no new keywords.
• Parse table: STATE_COUNT 30622 → 30703 (+0.3%), parser.c 41.6 MB → 41.7 MB.
• Independent of feat(grammar): procedural control flow in function and procedure bodies #371 to feat(grammar): PERFORM, EXECUTE, RETURN QUERY, INTO targets, DO and CALL #374.

Closes #364