planner: fix order by sub-query couldn't find outer correlated columns[DNM]

[AilinKid]

What problem does this PR solve?

Issue Number: close #26945

Problem Summary:

DROP TABLE IF EXISTS t1, t2;
CREATE TABLE t1 (a INT, b INT);
CREATE TABLE t2 (a INT, b INT);
INSERT INTO t1 VALUES (1, 1);
INSERT INTO t2 VALUES (1, 1);
SELECT one.a FROM t1 one ORDER BY (SELECT two.b FROM t2 two WHERE two.a = one.b);

What is changed and how it works?

just used to test CLA

fetch the correlated column in order-by subquery out to select fields, building it as an Auxiliary one, which will be stored as p.schema() (passing as outer schema when enter subquery) when we try to build order-by clause. Otherwise it couldn't find that correlated column.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

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1 out of 2 committers have signed the CLA.

✅ AilinKid
❌ arenatlx

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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/cef6ed94d04e7c1099c74e950c40369b4c8f0110