expression: fix casting REAL type to STRING type (#16975)

[ti-chi-bot]

This is an automated cherry-pick of #16975

What is changed and how it works?

Issue Number: Close #16974

ref pingcap/tidb#53129

What's Changed:

expression: fix casting REAL type to STRING type
- unify the behavior of converting real types to strings in tidb#53129 and tikv.
- use ryu lib in tikv to implement casting real type to str type.
- `if abs(num) >= 1e15 or (num is not zero and abs(num) < 1e-15)` then use decimal exponent format 

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)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Release note

Fix the incorrect result when casting REAL type to STRING type

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• gengliqi
• wshwsh12

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[solotzg]

ref pingcap/tidb#53207

[solotzg]

/cc @gengliqi

[solotzg]

/assign @solotzg

[solotzg]

/cc @wshwsh12

[gengliqi]

/merge

[ti-chi-bot]

@gengliqi: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

If you have any questions about the PR merge process, please refer to pr process.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

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

Commit hash: 24db5a2