[VECGEOM-375] Using 'constexpr' instead of just 'const'
This change was suggested by Philippe: to use 'constexpr' instead of just 'const' for the new tolerance constants in GenericKernelsForContainsAndInside(), recently merged into master.
This change was suggested by Philippe: to use 'constexpr' instead of just 'const' for the new tolerance constants in GenericKernelsForContainsAndInside(), recently merged into master.