types: fix type merge about bit type

[lzmhhh123]

Signed-off-by: lzmhhh123 lzmhhh123@gmail.com<!-- Thank you for contributing to TiDB!

PR Title Format:

1. pkg [, pkg2, pkg3]: what's changed
2. *: what's changed

-->

What problem does this PR solve?

Issue Number: close #23832

What is changed and how it works?

How it Works: make type merge infer for bit column compatible with MySQL 8.0

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Release note

• fix type merge about bit type.

[lzmhhh123]

/cc @XuHuaiyu @ichn-hu

[XuHuaiyu]

• The field_types_merge_rules in TiDB is the same as that defined in MySQL 5.7
• Why the result in MySQL 5.7 can also return the same result as 8.0 but with a different type?

mysql> select a from t union select 10;
Field   1:  `a`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  binary (63)
Length:     20
Max_length: 2
Decimals:   0
Flags:      BINARY


+------+
| a    |
+------+
| 10   |
| 1    |
| 2    |
+------+
3 rows in set (0.00 sec)

[lzmhhh123]

IMHO, the result of bit merge int is int looks much more reasonable. It's also the same as MySQL 8.0. We'd better not keep all consistent as MySQL 5.7 brainlessly.

[XuHuaiyu]

/lgtm

[wshwsh12]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• 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 writing /lgtm in a comment.
Reviewer can cancel approval by writing /lgtm cancel in a comment.

[wshwsh12]

/merge

[ti-chi-bot]

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

Commit hash: 257ddaa

[wshwsh12]

/run-all-tests

[wshwsh12]

/run-unit-test

[ti-srebot]

cherry pick to release-4.0 in PR #24026

[ti-srebot]

cherry pick to release-5.0 in PR #24027