An initial implementation of EXISTS

[joka921]

This implements EXISTS via a new ExistsJoin operation (which can be seen in the "Analysis" tree when executing a query). The implementation has the following limitations, which will be addressed in future PRs:

1. The ExistsJoin operation is about 20% slower than a comparable ordinary Join operation (in particular, the former does not yet use ad_utility::callFixedSize)
2. The ExistsJoin operation is not yet lazy
3. TODO: how are FILTERs inside the EXIST referring to variables outside the EXIST handled?

TODO: ...

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 16 lines in your changes missing coverage. Please review.

Project coverage is 89.92%. Comparing base (acb6633) to head (5294357).

Files with missing lines	Patch %	Lines
src/engine/sparqlExpressions/ExistsExpression.h	58.82%	6 Missing and 1 partial ⚠️
src/engine/MultiColumnJoin.cpp	20.00%	4 Missing ⚠️
src/engine/ExistsJoin.cpp	97.08%	2 Missing and 1 partial ⚠️
src/engine/ExistsJoin.h	75.00%	1 Missing ⚠️
src/util/JoinAlgorithms/FindUndefRanges.h	95.45%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1703      +/-   ##
==========================================
+ Coverage   89.86%   89.92%   +0.05%     
==========================================
  Files         389      392       +3     
  Lines       37308    37476     +168     
  Branches     4204     4218      +14     
==========================================
+ Hits        33527    33699     +172     
+ Misses       2485     2478       -7     
- Partials     1296     1299       +3     

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[sparql-conformance]

Conformance check passed ✅

Test Status Changes 📊

Number of Tests	Previous Status	Current Status
19	Failed	Passed

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=52943570743cb6c9db292f6331e1b8304ab32379&prev=acb6633debc7341985341aff147b5038cc8d951b

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud