parser: support common table expression (WITH clause)

[LordofAvernus]

What problem does this PR solve?

WITH ... AS (...) SELECT/INSERT/UPDATE/DELETE (MySQL 8.0 CTE) fails to parse on the
current release-4.0.2, e.g.:

WITH cte AS (SELECT 1 AS id) SELECT * FROM cte
=> line 1 column 4 near "WITH cte AS (SELECT 1 AS id) SELECT * FROM cte"

Downstream consumers (SQLE) therefore cannot build an AST for CTE statements and end up
misclassifying them (e.g. a CTE + SELECT being reported as DDL instead of DQL).

What is changed and how it works

• ast: add CommonTableExpression and WithClause (IsRecursive, CTEs), with
  Restore and Accept implemented so the clause round-trips.
• ast: add an optional With *WithClause field to SelectStmt, InsertStmt,
  UpdateStmt and DeleteStmt; Restore/Accept of each statement handle it when
  non-nil, so behaviour is unchanged for statements without a WITH clause.
• parser.y: split each DML rule into a *NoWith variant and let the
  WithClause-prefixed rule reuse it; add WithClause, WithList, CommonTableExpr,
  IdentList, IdentListWithParenOpt.
• misc.go / parser.y: add the RECURSIVE token.
• parser.go: regenerated from parser.y.

Compatibility note

RECURSIVE is introduced as a reserved keyword, matching MySQL 8.0 and upstream
TiDB's parser. As a consequence recursive can no longer be used as a bare identifier:

CREATE TABLE t (recursive int)   -- parsed before, rejected now
SELECT recursive FROM t          -- parsed before, rejected now

If keeping recursive usable as an identifier matters more than matching MySQL 8.0
behaviour here, please say so and I will rework it as an unreserved keyword.

Tests

• New cte_test.go covering SELECT/INSERT/UPDATE/DELETE with a WITH clause,
  column name lists, multiple CTEs, WITH RECURSIVE, invalid inputs, plus AST-level
  assertions. Restore round-trip is verified through the existing RunTest helper.
• Full suite (go test ./...) shows no new failures: the 3 pre-existing failures
  (TestKeywordConsistent, TestscanString, TestDMLStmt) and the ast vet failure
  are identical on b6199b7 without this change.

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