expression: handle duration type infer in least and greatest (#22271)

[qw4990]

cherry-pick #22271 to release-4.0
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/22421

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

git push git@github.com:ti-srebot/tidb.git pr/22421:release-4.0-4658536793d5

---

What problem does this PR solve?

Issue Number: close #22200

Problem Summary:

What is changed and how it works?

This pull request compares duration as string while they are formalized which will prevent panicking while encountering a non-handled duration type infer.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Side effects

• Performance regression
  • Consumes more CPU
  • Consumes more MEM
• Breaking backward compatibility

Release note

• expression: handle duration type infer in least and greatest

[qw4990]

/run-all-tests

[winoros]

lgtm

[time-and-fate]

LGTM