planner: notify skyline pruning of index statistics availability

[terry1purcell]

Extend support for skyline pruning recognition of index without statistics to existing rules.

By passing the "pseudo" result of the index from the CompareCandidates function for the "successful" index - it allows the later checking in SkyLinePruning to keep that index to prioritize above a table scan if tidb_opt_prefer_range_scan global variable is set.

This change is a minor addition to address prior customer concerns that a newly created index that does NOT yet have statistics may be selected by the existing CompareCandidates code - and the index WITH statistics is pruned. But the cost of the index that used defaults (since no statistics) may have a higher cost than tablescan.

What problem does this PR solve?

Issue Number: close #57948

Problem Summary:

What changed and how does it work?

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

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[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.3397%. Comparing base (aabd3ac) to head (bd6f4a7).
Report is 33 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #59110        +/-   ##
================================================
+ Coverage   73.0284%   73.3397%   +0.3113%     
================================================
  Files          1683       1689         +6     
  Lines        466099     481065     +14966     
================================================
+ Hits         340385     352812     +12427     
- Misses       104791     106579      +1788     
- Partials      20923      21674       +751     

Flag	Coverage Δ
integration	42.9797% <36.3636%> (?)
unit	72.2378% <72.7272%> (+0.0306%)	⬆️

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Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	44.1372% <ø> (-1.1776%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, winoros

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-23 03:18:15.545110075 +0000 UTC m=+323622.876029478: ☑️ agreed by hawkingrei.
• 2025-01-26 02:22:21.797797376 +0000 UTC m=+579469.128716780: ☑️ agreed by winoros.