Externals Update, 24.0 branch (2024.04.22.)

Updated all projects to atlasexternals-2.1.16. The complete changeset wrt. atlasexternals-2.1.10 is (atlasexternals@2.1.10...2.1.16):

• Introduced FindHighFive.cmake for the correspondingly named external;
• Changed External/onnxruntime to download a pre-built binary of ONNXRuntime instead of building it itself;
  • Updated Findonnxruntime.cmake to handle the different header layout coming with the pre-built binaries;
• Upgraded GeoModel to version 5.3.0 (no effect on 24.0);
• Set CMP0069 to NEW, to allow for convenient link time optimizations in the ATLAS projects;
• Upgraded Geant4 to version 10.6.3.13;
• Made it possible to turn on LTO for the Geant4 and VecGeom builds.

This all is mainly needed for ATLASSIM-6058, to speed up G4. But it shall also help with ATLINFR-5341 because of the ONNX updates. 🤔

The most controversial part, I believe, is that the MR switches off our GCC checkers. Since as we discussed in ATLASSIM-6058 with @ssnyder, that code doesn't work with LTO just yet. (But hopefully soon.) So for now I propose to turn it off for Athena-24.0. But I'm open to a discussion about this. 🤔