Simplify CMake config and optimize includes

[RobinTF]

In particular:

• Clean up the usage of the FETCH_CONTENT module by using its builtin functionality instead of manual hacks (see the JSON and ANTLR dependencies for details).
• Make the includes of the ANTLR and ABSL submodules (which use macros that collide with our own) more robust.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.25%. Comparing base (77ac964) to head (9937811). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1618 +/- ## ========================================== + Coverage 89.24% 89.25% +0.01% ========================================== Files 374 375 +1 Lines 35315 35315 Branches 3988 3988 ========================================== + Hits 31518 31522 +4 + Misses 2503 2501 -2 + Partials 1294 1292 -2 ```

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[RobinTF]

@joka921

Alsom, in the macos workflow it says env.build-type once, and matrix.build-type twice. It has to be always env.build-type, thant is the issue there.

I'm pretty sure you mean it has to be matrix.build-type

[sparql-conformance[bot]]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=99378114e056076f2ffb7fc5071fed612d2e0c77&prev=77ac964e9de37c10142bc19735d19fbb0c02ccc6

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
D Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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