CMakeLists updates in ForwardDetectors

Vakhtang Tsulaiarequested to merge
tsulaia/athena:masterd-fd-gm-cmake into master

Updated ForwardDetectors packages to use FindGeoModel.cmake. Which was introduced to serve the new GeoModel uni-project, which was introduced into our build with !39900 (merged).

Bonus:

  • Turned AFP_GeoModel and ZDC_GeoM into component-only packages
  • Turned ForwardRegionGeoModel into interface + component package

CC: @rbianchi

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