Fix derived table bug

[GuptaManan100]

Description

This PR fixes the issue described in #15830.
While working on fixing the derived table query, it was noticed that select * from (select u.foo * ue.bar from user u join user_extra ue) as dt wasn't working on main even before #15588 was merged but still #15588 made it worse (as in the plan became even more wrong if that makes sense).

This PR fixes this issue and after the changes in this PR, that query works as intended. There are 2 changes in this PR -

1. We can't override the original expression when we see a derived table, because overriding the original with a column name causes issues with breaking the expression since a column name can't be split. At the same time, we don't want to lose the information about the column name either. So we now store this information in a newly introduced field called DTColumn. We further change planning of offsets to check for the DTColumn value. Since we know the underlying source has a field with this name, we get it from there.

2. The other bug present in main even before Make sure derived table column names are handled correctly #15588 was merged, was around projection pushing wherein a new projection would totally override the join columns. This led to the information about the splitting of columns being forgotten and then the same problem wherein we can't split an aliased expression. The fix is to just reuse the joinColumns if they're already populated.

Related Issue(s)

• Fixes Bug Report: Recent changes causing other queries to fail #15830

Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.44%. Comparing base (cf3acaa) to head (4b0edc7).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15831      +/-   ##
==========================================
+ Coverage   68.41%   68.44%   +0.02%     
==========================================
  Files        1558     1559       +1     
  Lines      196353   196511     +158     
==========================================
+ Hits       134337   134501     +164     
+ Misses      62016    62010       -6     

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