Refactor Join Predicate Handling in Planner

[systay]

Description

This pull request refactors the planner to enhance join predicate management. Previously, we would skip already pushed down predicates when merging join inputs into a single route and then push down new predicates. With this change, we’re introducing a predicate tracker to manage and adjust the predicates that have been pushed to the right-hand side of the join. This simplifies the code and we can get use smaller operator trees and less state in the planning context.

Related Issue(s)

This depends on #17875

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

Review Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 83.46457% with 21 lines in your changes missing coverage. Please review.

Project coverage is 67.52%. Comparing base (0af627a) to head (ebeae68).

Files with missing lines	Patch %	Lines
go/vt/vtgate/semantics/table_set.go	0.00%	13 Missing ⚠️
...gate/planbuilder/operators/predicates/predicate.go	66.66%	6 Missing ⚠️
go/vt/vtgate/planbuilder/operators/join_merging.go	88.23%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17877   +/-   ##
=======================================
  Coverage   67.51%   67.52%           
=======================================
  Files        1595     1597    +2     
  Lines      259640   259652   +12     
=======================================
+ Hits       175292   175323   +31     
+ Misses      84348    84329   -19     

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