executor: use EncodeKey to encode groupkey in StreamAggExec (#49974)

[ti-chi-bot]

This is an automated cherry-pick of #49974

What problem does this PR solve?

Issue Number: close #49902

Problem Summary:

What changed and how does it work?

Use EncodeKey function to encode the groupkey within StreamAggExec. This approach is necessary as it considers collation when aggregating the result.

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.

Fixed the issue with StreamAgg that caused incorrect results due to mishandling collation ci.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, XuHuaiyu

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-08 08:31:44.020961788 +0000 UTC m=+259293.605215493: ☑️ agreed by XuHuaiyu.
• 2024-01-08 09:04:27.325451359 +0000 UTC m=+261256.909705047: ☑️ agreed by AilinKid.