Extend SQL coverage: triggers, window frames, roles/RLS, GRANT, position(), deferrable FKs, exact numeric literals

[sanketsahu]

Intent

This extends pgsql-ast-parser to parse a range of common PostgreSQL syntax that wasn't
yet supported. It was developed while evolving pg-mem toward fuller Postgres
conformance — see the companion PR oguimbal/pg-mem#476, which consumes these AST additions.

Every addition follows the repo's conventions: grammar rule → AST node → toSql
round-trip → spec.

What's added

• Window frame clauses — ROWS | RANGE | GROUPS with BETWEEN … AND … and the
  UNBOUNDED PRECEDING/FOLLOWING, CURRENT ROW, <n> PRECEDING/FOLLOWING bounds
  (CallOver.frame, CallOverFrame, FrameBound).
• CREATE TRIGGER / DROP TRIGGER — CREATE [CONSTRAINT] TRIGGER, BEFORE | AFTER | INSTEAD OF, INSERT | UPDATE [OF cols] | DELETE | TRUNCATE (OR-ed), ON table,
  FOR EACH ROW | STATEMENT, WHEN (...), EXECUTE FUNCTION | PROCEDURE f(...)
  (CreateTriggerStatement, TriggerEvent); and DROP TRIGGER [IF EXISTS] name ON table [CASCADE | RESTRICT] (DropTriggerStatement, with onTable).
• EXECUTE <name>(args) to run a PREPAREd statement (ExecuteStatement). PREPARE
  and DEALLOCATE were already parsed; EXECUTE was the missing piece.
• TABLESPACE clause on CREATE TABLE (CREATE INDEX already supported it). Physical
  storage is meaningless to most AST consumers, but it appears in pg_dump output.
• CREATE DOMAIN — a base type with NOT NULL / NULL / CHECK constraints and an
  optional DEFAULT (CreateDomainStatement, DomainConstraint).
• RETURNS SETOF <type> on CREATE FUNCTION (a setof flag on the statement).
• #> JSON path operator (complements the existing #>>).
• Composite-type field access — (expr).field, the standard syntax for reading a
  field off a parenthesized composite/row value (e.g. (center).x, (row(1,2)).f1).
  ExprMember.op is widened to include '.'. No grammar ambiguity introduced.
• MERGE (PG 15+) — MERGE INTO target USING source ON cond WHEN [NOT] MATCHED [AND cond] THEN { UPDATE SET … | DELETE | INSERT [(cols)] VALUES (…) | INSERT DEFAULT VALUES | DO NOTHING }. New MergeStatement / MergeAction AST, merge.ne grammar,
  to-sql + ast-mapper support.
• Declarative partitioning — PARTITION BY {RANGE|LIST|HASH} (cols) on CREATE TABLE,
  and CREATE TABLE child PARTITION OF parent FOR VALUES { FROM (..) TO (..) | IN (..) | WITH (MODULUS m, REMAINDER r) } | DEFAULT. New PartitionBy / PartitionOf /
  PartitionBound* AST; bare MINVALUE/MAXVALUE in a range bound resolved without
  grammar ambiguity.
• INTERSECT / EXCEPT — the UNION grammar/AST is widened to the full set-operation
  family (SetOperationType: union/intersect/except, each with optional ALL).
• IS DISTINCT FROM / IS NOT DISTINCT FROM null-safe comparison operators (new
  expr_is alternative; EqualityOperator widened).
• week / decade / century / millennium units in interval literals (normalized to
  days/years).
• GROUP BY GROUPING SETS (...) (emitted as a grouping sets call alongside the
  existing rollup/cube calls).
• position(substring IN string) special syntax (new ExprPosition node). The
  generic position(...) call form is rejected to avoid an ambiguity with IN.
• Roles — CREATE ROLE/CREATE USER, DROP ROLE, SET [SESSION|LOCAL] ROLE,
  RESET.
• Row-level security DDL — CREATE/DROP POLICY, and ALTER TABLE … {ENABLE | DISABLE | FORCE | NO FORCE} ROW LEVEL SECURITY.
• GRANT / REVOKE — table/sequence privileges, plus ON SCHEMA | DATABASE | FUNCTION | PROCEDURE | ROUTINE, ON ALL {TABLES|SEQUENCES|FUNCTIONS|ROUTINES} IN SCHEMA, and ALTER ROLE / ALTER DEFAULT PRIVILEGES.
• NOTIFY / LISTEN / UNLISTEN (NotifyStatement, ListenStatement,
  UnlistenStatement).
• COMMENT ON POLICY / COMMENT ON FUNCTION.
• ALTER COLUMN ... TYPE ... USING <expr> — the conversion expression is captured
  on AlterColumnSetType.using.
• CREATE INDEX ... INCLUDE (cols) — covering-index payload columns
  (CreateIndexStatement.include).
• CREATE FUNCTION ... SECURITY DEFINER | INVOKER (CreateFunctionStatement.security).
• Comment-only / whitespace-only input now parses to [] rather than throwing,
  matching Postgres accepting an empty command string.
• Dollar-quoted strings with named tags — $tag$…$tag$ (not just $$…$$) now lex as
  string literals, both as expression values (e.g. INSERT … VALUES ($body$…$body$)) and
  as DO/function bodies. The matching close tag is resolved in the lexer.next wrapper
  (a moo rule can't backreference the tag).
• Array slicing — arr[lo:hi], arr[:hi], arr[lo:] (ExprArraySlice with optional
  from/to), complementing the existing arr[i] indexing.
• DEFERRABLE [INITIALLY DEFERRED | IMMEDIATE] on foreign keys.
• Optional column list on WITH RECURSIVE (WITH RECURSIVE t AS …).
• Exact numeric-literal precision — ExprInteger/ExprNumeric now carry an optional
  valueText holding the exact source digits. JS numbers lose precision above 2^53 and
  for many decimals, so 9007199254740993 and 1.005 were being corrupted at parse
  time. The field is backward-compatible: it is absent unless the literal actually
  needs it (large ints, fractional/exponent numerics), so existing consumers and ASTs are
  unchanged.

Tests / coverage

• All new syntax has round-tripping specs (parse → toSql → re-parse is stable, per the
  existing checkTree* harness). 836 tests passing.
• Each feature was additionally validated against PostgreSQL 16 through pg-mem's
  differential conformance harness (same SQL run on pg-mem and a real Postgres, results
  diffed).

Bundle-size impact

Compiled grammar only grows a little, and there are no new dependencies:

bundle (gzipped)	before	after	delta
pgsql-ast-parser	48.9 KB	55.5 KB	+6.6 KB (~+13%)

(measured on the compiled lib/index.js, gzipped, this branch vs upstream master.)

Independence

This PR is self-contained and can be merged and released on its own. The companion pg-mem PR (oguimbal/pg-mem#476) depends on these AST additions (and on this being published), not the other way
around.