charset: alias utf8 and utf8mb3

[dveeden]

What problem does this PR solve?

Issue Number: close #26226

close #31790

Problem Summary:

MySQL recognizes both utf8 and utf8mb3. These are aliases for the legacy 3-byte UTF-8 (replaced by utf8mb4).

Tables and columns created as utf8 will in recent versions of MySQL 8.0 will output utf8mb3 in the output of SHOW CREATE TABLE. This complicates migration to TiDB.

What is changed and how it works?

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

Please refer to Release Notes Language Style Guide to write a quality release note.

TiDB now recognizes both `utf8` and `utf8mb3` to as the legacy 3-byte character set encoding

[Defined2014]

This affects product behavior and may require PM decision. /cc @bb7133 @easonn7

[lance6716]

thanks for the PR! really helps the data migration scenario

[songrijie]

As per doc of MySQL, this PR makes good point to translate "utf8mb3" to the legacy 3-byte UTF-8.

Historically, MySQL has used utf8 as an alias for utf8mb3; beginning with MySQL 8.0.28, utf8mb3 is used exclusively in the output of SHOW statements and in Information Schema tables when this character set is meant.

At some point in the future utf8 is expected to become a reference to utf8mb4. To avoid ambiguity about the meaning of utf8, consider specifying utf8mb4 explicitly for character set references instead of utf8.

Prior to MySQL 8.0.29, instances of utf8mb3 in statements were converted to utf8. In MySQL 8.0.30 and later, the reverse is true, so that in statements such as SHOW CREATE TABLE or SELECT CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.COLUMNS or SELECT COLLATION_NAME FROM INFORMATION_SCHEMA.COLUMNS, users see the character set or collation name prefixed with utf8mb3 or utf8mb3_.

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, tangenta

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-06-14 03:58:03.480063059 +0000 UTC m=+144479.894667119: ☑️ agreed by tangenta.
• 2023-06-14 09:32:42.887537222 +0000 UTC m=+164559.302141302: ☑️ agreed by Defined2014.