Externals Update, master branch (2022.01.26.)

Updated all projects to atlasexternals-2.0.126. The list of changes wrt. atlasexternals-2.0.125 is the following (atlasexternals@2.0.125...2.0.126):

• Added lark 1.0.0 (a parsing toolkit for Python) to PyModules (thanks to @ponyisi);
• Introduced find-modules for protobuf, boto3, botocore, jmespath and s3transfer in AtlasLCG (thanks to @sanchezj);
  • Made lcg_python_external_module(...) a bit more robust in support of these new modules;
• Introduced a package for building VecGeom, and updated the Geant4 build to use this build of VecGeom itself (thanks to @mbandier and @bmorgan).

Because of the Geant4 update, this required both full-build and full-unit-tests.