executor, util: reset offsets and nullBitMap for MutRow when setting new values (#30265)

[ti-srebot]

cherry-pick #30265 to release-5.1
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/30390

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

git push git@github.com:ti-srebot/tidb.git pr/30390:release-5.1-70d29735e636

---

What problem does this PR solve?

Issue Number: close #29947

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test

Side effects

N/A

Documentation

N/A

Release note

Fix the problem that window function may return different results when using transaction or not.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• guo-shaoge
• wshwsh12

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[ti-srebot]

/run-all-tests

[ti-srebot]

@XuHuaiyu you're already a collaborator in bot's repo.

[XuHuaiyu]

/merge

[ti-chi-bot]

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

Commit hash: 08a7a51

[bb7133]

/merge

[ti-chi-bot]

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

Commit hash: 62f0e16

[XuHuaiyu]

/merge

[ti-chi-bot]

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

Commit hash: eff14dc

[ti-chi-bot]

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