Fix Scale and length handling in CASE and JOIN bind variables

[GuptaManan100]

Description

This PR fixes a part of the problem described in #15784 (comment).

This PR fixes 2 issues -

1. Correctly handle scale and length for decimal in case implementation of evalengine.
2. Fix the bind variable passed down in JOIN engine primitive for DECIMAL type, taking the scale and length into account.

Related Issue(s)

• Fixes part of the problem in Bug Report: TPCH query returns incorrect precision count in the fields #15784

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• 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

Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 72.22222% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 68.43%. Comparing base (4c2df48) to head (94fe5b1).
Report is 2 commits behind head on main.

Files	Patch %	Lines
go/mysql/json/parser.go	0.00%	4 Missing ⚠️
go/vt/vtgate/evalengine/eval_enum.go	0.00%	4 Missing ⚠️
go/vt/vtgate/evalengine/eval_set.go	0.00%	4 Missing ⚠️
go/vt/vtgate/evalengine/eval_tuple.go	0.00%	4 Missing ⚠️
go/vt/vtgate/engine/join.go	57.14%	3 Missing ⚠️
go/vt/vtgate/evalengine/eval.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15787      +/-   ##
==========================================
- Coverage   68.44%   68.43%   -0.01%     
==========================================
  Files        1558     1558              
  Lines      195822   195885      +63     
==========================================
+ Hits       134025   134049      +24     
- Misses      61797    61836      +39     

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[dbussink]

Please make sure to merge / rebase since the signature of this function has changed.

[dbussink]

Does this logic apply to other usages of the typeAggregation as well? And should this really be part of typeAggregation therefore instead? Seems like that might be more appropriate to refactor it into that?

[GuptaManan100]

I have made the required changes. I wasn't sure what the length and scale for other data types looks like, so I just passed 0 from everywhere.