execution: add default value logic for scalar final agg in mock mpp executor

[AilinKid]

What problem does this PR solve?

Issue Number: close #50893

Problem Summary:

What changed and how does it work?

previously mpp handler don't pay any attention to agg-pb‘s agg mode, which is to say they don't care about whether agg is finalAgg or partial ones. While for scalar finalAgg (when there is no groupKeys, itself is a scalar agg, which should be judged before running), default value logic filling is necessary, referred from current tidb execution and real tiflash logic. While for scalar partialAgg, filling default value logic is NOT necessary.

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

[ti-chi-bot]

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[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 86.95652% with 6 lines in your changes missing coverage. Please review.

Project coverage is 55.8514%. Comparing base (1621e0f) to head (b3741f5).
Report is 1633 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #50982         +/-   ##
=================================================
- Coverage   70.5452%   55.8514%   -14.6938%     
=================================================
  Files          1466       1576        +110     
  Lines        434768     616408     +181640     
=================================================
+ Hits         306708     344273      +37565     
- Misses       108772     249383     +140611     
- Partials      19288      22752       +3464     

Flag	Coverage Δ
integration	38.2950% <60.8695%> (?)
unit	71.6466% <86.9565%> (+1.2977%)	⬆️

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

Components	Coverage Δ
dumpling	54.1120% <ø> (ø)
parser	∅ <ø> (∅)
br	51.5377% <ø> (+5.8344%)	⬆️

[AilinKid]

/cc @hawkingrei zhen

[ti-chi-bot]

@AilinKid: GitHub didn't allow me to request PR reviews from the following users: zhen.

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/cc @hawkingrei zhen

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[AilinKid]

/retest-required

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/retest-required

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[ti-chi-bot]

PR needs rebase.

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[ti-chi-bot]

@AilinKid: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-br-integration-test	b3741f5	link	true	/test pull-br-integration-test
pull-lightning-integration-test	b3741f5	link	true	/test pull-lightning-integration-test

Full PR test history. Your PR dashboard.

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