planner: Preference index stats if they exist (WIP)

[terry1purcell]

What problem does this PR solve?

Issue Number: close #xxx

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

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None

[tiprow]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.4814%. Comparing base (35f329d) to head (5559622).
Report is 11 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58689        +/-   ##
================================================
+ Coverage   73.1026%   73.4814%   +0.3788%     
================================================
  Files          1677       1677                
  Lines        463652     463940       +288     
================================================
+ Hits         338942     340910      +1968     
+ Misses       103883     102195      -1688     
- Partials      20827      20835         +8     

Flag	Coverage Δ
integration	42.8544% <100.0000%> (?)
unit	72.2645% <100.0000%> (-0.0201%)	⬇️

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Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	45.4515% <ø> (-0.3101%)	⬇️

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[terry1purcell]

Despite code allowing missing index stats to ignore available column stats - I could not reproduce a testcase to expose this