external: range job keys and region split keys are 2 concepts (part 1) (#55659)

[ti-chi-bot]

This is an automated cherry-pick of #55659

What problem does this PR solve?

Issue Number: ref #55374

Problem Summary:

What changed and how does it work?

This is the first part of making job range keys and region split keys 2 different concetps, and it's only related to external engine changing. In next PR I'll change how lighting local backend will use them.

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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[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.3@1a0c3ac). Learn more about missing BASE report.

Additional details and impacted files

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Flag	Coverage Δ
integration	37.2140% <71.8750%> (?)
unit	71.8445% <61.4583%> (?)

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

Components	Coverage Δ
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parser	∅ <0.0000%> (?)
br	52.5744% <0.0000%> (?)