codec: Don't convert set or enum datum to float64 when encoding them (#32308)

[ti-srebot]

cherry-pick #32308 to release-5.0
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/32351

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

git push git@github.com:ti-srebot/tidb.git pr/32351:release-5.0-886650b58265

---

Signed-off-by: ekexium ekexium@gmail.com

What problem does this PR solve?

Issue Number: close #32302

Problem Summary:

When a enum or a set datum is encoded, it's uint64 value is converted to float64 and then converted back to uint64, resulting in the loss of lower bits.

What is changed and how it works?

Use the original Value, don't convert.

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

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• MyonKeminta
• cfzjywxk

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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.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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[ti-srebot]

/run-all-tests

[ekexium]

/run-mysql-test

[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

• https://prow.tidb.io/command-help#cherrypick
• https://book.prow.tidb.net/#/plugins/cherrypicker

You can find more details at:

• https://internals.tidb.io/t/topic/785