Update master branch to atlasexternals 2.0.53
Update all projects to https://gitlab.cern.ch/atlas/atlasexternals/-/tags/2.0.53
Update(s) since 2.0.52:
- Updated the environment setup script to be a bit leaner/faster;
- Fixed how the OptDbg package builds would use the project's README.txt file;
- Added FindVBFNLO.cmake to AtlasLCG.
The first change (atlasexternals!586 (merged)) is the only non-trivial item here and we need to carefully check that things still work as expected. Hopefully the CI should cover most use-cases. But another careful check once in the nightly is also required.
cc @akraszna