WIP: VECGEOM-577: Prefix VecGeom related CMake options with "VECGEOM_"
VecGeom does not prefix its CMake options with the project name, which can cause confusion:
- When viewing in CMake GUIs as they are mixed in with others
- Potential overlaps with other client options/environment
Prefix all Vecgeom specific CMake variables with "VECGEOM_" to distinguish them from other options such as "CMAKE_" or "CUDA_". Update all internal uses with the new name.
Update names in Install document. Requires changes to testing as well, but best done through iteration on CI.
This is a breaking change to build interface for packagers etc, hence the JIRA ticket and marking as WIP.