Fix(optimizer): propagate recursive CTE source to children scopes early

[georgesittas]

Before:

>>> from sqlglot import parse_one
>>> from sqlglot.optimizer.qualify import qualify
>>>
>>> sql = """
... with recursive t as (
...   select 1 as x
...   union all
...   select x + 1 from t as child where x < 10
... )
... select * from t
... """
>>>
>>> expr = parse_one(sql)
>>> print(qualify(expr, infer_schema=False).sql(pretty=True))
sqlglot.errors.OptimizeError: Column '"x"' could not be resolved

After:

>>> from sqlglot import parse_one
>>> from sqlglot.optimizer.qualify import qualify
>>>
>>> sql = """
... with recursive t as (
...   select 1 as x
...   union all
...   select x + 1 from t as child where x < 10
... )
... select * from t
... """
>>>
>>> expr = parse_one(sql)
>>> print(qualify(expr, infer_schema=False).sql(pretty=True))
WITH RECURSIVE "t" AS (
  SELECT
    1 AS "x"
  UNION ALL
  SELECT
    "child"."x" + 1 AS "_col_0"
  FROM "t" AS "child"
  WHERE
    "child"."x" < 10
)
SELECT
  "t"."x" AS "x"
FROM "t" AS "t"