expresssion: determine the field type of control function with enum type (#24830)

[ti-srebot]

cherry-pick #24830 to release-5.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/24915

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git push [email protected]:ti-srebot/tidb.git pr/24915:release-5.0-2f96bc7502ac

---

What problem does this PR solve?

Issue Number: close #24543

Problem Summary:

What is changed and how it works?

Proposal: xxx

What's Changed:
Determine the field type of control function with enum type. If the return fieldtype is enum, we can use the evaltype to determine the fieldtype.

How it Works:

Related changes

Check List

Tests

• Unit test
• Integration test

Side effects

Release note

• If unexpect panic for control function

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-srebot]

/run-all-tests

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