session, ddl: amend txn correctly when "modify column" needs reorg data with tidb_enable_amend_pessimistic_txn=on. (#26269)

[ti-srebot]

cherry-pick #26269 to release-5.1
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/26273

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/26273:release-5.1-6e72be0013da

---

What problem does this PR solve?

Issue Number: close #26203

Problem Summary:
Columns exist in an intermediate state when we support modifying the column type (which requires reorg the data). So we can't just check the public state columns when we check whether the operation is amendable.

What is changed and how it works?

Proposal: xxx

What's Changed:

Use WritableCols instead of Cols.

Check List

Tests

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

Release note

• amend transactions correctly when "modify column" needs reorg data with tidb_enable_amend_pessimistic_txn=on.

[ti-srebot]

/run-all-tests

[zimulala]

PTAL @cfzjywxk

[cfzjywxk]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• cfzjywxk

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[zimulala]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 4fd6073

[AilinKid]

/merge