expression: fix charset conversion warning and error behavior (#51191)

[ti-chi-bot]

This is an automated cherry-pick of #51191

What problem does this PR solve?

Issue Number: close #50295

Problem Summary:

The error cannotConvertString should have three different behaviors:

1. Explicit cast, and SQL_MODE is strict: it'll return NULL and add a warning.
2. Explicit cast, and SQL_MODE is not strict: it'll return truncated string and add a warning.
3. Implicit cast: it'll return an error.

TiDB returns error in all cases, so it's not compatible.

What changed and how does it work?

Fix the behavior of from_binary function. Now it's only fixed on TiDB, and will need some modification on TiKV as well.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

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.

None

[YangKeao]

LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-13 08:31:36.946457442 +0000 UTC m=+1469250.703593010: ☑️ agreed by Defined2014.
• 2024-05-13 08:32:24.623795144 +0000 UTC m=+1469298.380930720: ☑️ agreed by YangKeao.

[codecov]

Codecov Report

Attention: Patch coverage is 56.25000% with 14 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (release-8.1@2a04b9c). Click here to learn what that means.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #53227   +/-   ##
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Flag	Coverage Δ
unit	71.1536% <56.2500%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	40.9806% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, YangKeao, zanmato1984

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• OWNERS [Defined2014,YangKeao,zanmato1984]
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