Fix segfault on CAggs with multiple JOINs

[fabriziomello]

Creating or changing to realtime a Continuous Aggregate with multiple joins was leading to a segfault.

Fixed it by dealing properly with the varno when creating the Quals for the union view in realtime mode.

Also get rid of some left over when we relaxed the CAggs join restrictions in #7111.

Disable-check: force-changelog-file
Disable-check: commit-count

[codecov]

Codecov Report

Attention: Patch coverage is 93.93939% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.77%. Comparing base (59f50f2) to head (57f7b71).
Report is 264 commits behind head on main.

Files	Patch %	Lines
tsl/src/continuous_aggs/common.c	84.61%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7146      +/-   ##
==========================================
+ Coverage   80.06%   81.77%   +1.70%     
==========================================
  Files         190      203      +13     
  Lines       37181    37960     +779     
  Branches     9450     9845     +395     
==========================================
+ Hits        29770    31042    +1272     
+ Misses       2997     2965      -32     
+ Partials     4414     3953     -461     

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[timescale-automation]

Automated backport to 2.15.x not done: cherry-pick failed.

Git status

HEAD detached at origin/2.15.x
You are currently cherry-picking commit 95acaa406.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   tsl/src/continuous_aggs/common.c
	modified:   tsl/src/continuous_aggs/common.h
	modified:   tsl/test/expected/cagg_repair-14.out
	modified:   tsl/test/expected/cagg_repair-15.out
	modified:   tsl/test/expected/cagg_repair-16.out

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   tsl/src/continuous_aggs/finalize.c
	both modified:   tsl/test/expected/cagg_joins.out
	both modified:   tsl/test/sql/cagg_joins.sql

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