fix(e6): emit plain LATERAL for lateral subqueries, not LATERAL VIEW

[tkaunlaky-e6]

Problem

E6.Generator.lateral_sql unconditionally set view=True on every Lateral node and always emitted LATERAL VIEW. So a standard LATERAL (subquery) (a correlated derived table) was rendered as LATERAL VIEW (subquery) — invalid in every dialect, since LATERAL VIEW requires a generator function, not a subquery. Nothing to do with explode/arrays; any plain lateral subquery hits it.

in : SELECT * FROM t1 LEFT JOIN LATERAL (SELECT x FROM t2 WHERE t2.a = t1.a) s ON TRUE
out: SELECT * FROM t1 LEFT JOIN LATERAL VIEW (SELECT ...) AS s ON TRUE     -- unparseable

in : SELECT * FROM t1, LATERAL (SELECT x FROM t2 WHERE t2.a = t1.a) s
out: SELECT * FROM t1 CROSS JOIN LATERAL VIEW (SELECT ...) AS s            -- unparseable

Root cause

The parser already distinguishes the two — a Spark LATERAL VIEW <generator> gets view=True; a plain LATERAL (subquery) does not. The base Generator.lateral_sql branches on that flag (view → LATERAL VIEW, else plain LATERAL via lateral_op). The e6 override discarded the flag and forced LATERAL VIEW on everything.

Fix

Guard before forcing the view flag: when the lateral wraps an exp.Subquery and view is not already set, delegate to the base generator (plain LATERAL). LATERAL VIEW / explode laterals are untouched.

if not expression.args.get("view") and isinstance(expression.this, exp.Subquery):
    return super().lateral_sql(expression)

Validation

• Live E6 engine: ... CROSS JOIN LATERAL (SELECT 2 AS x) t and ... LEFT JOIN LATERAL (...) ON TRUE parse and return rows; the old LATERAL VIEW (subquery) fails with Encountered "JOIN" ... expecting "APPLY".
• Coverage: all 37 LATERAL (subquery) queries in the migration run now emit plain LATERAL (0 still produce the invalid form).
• tests/dialects/test_e6.py: 59 passed / 901 subtests, incl. 2 new lateral-subquery regression cases; LATERAL VIEW EXPLODE unchanged.

Root-cause analysis and fix by Atharv Rastogi.