const*
const*
Use const geometry in TrackerInteractionGeometry

Converted to be compatible with changes to geometry to only give
const access to objects.
Use const geometry in SeedingLayerSetsBuilder

Converted to be compatible with changes to geometry to only give
const access to objects.
Make all DetLayer accesses const

When returning or passing a DetLayer as an argument to a member
function use const.
Make all usage of DetLayer classes const

The interface to access DetLayer classes is now always const. This
commit updates the client code to match that change.
Make MuonDetLayerGeometry only give const access to DetLayers

Changed the interface to MuonDetLayerGeometry to only give const
access to the data it holds. This is needed to enforce thread-safety.
All clients were updated to adapt to the new interface.

This change is part of the GeometricSearchTracker change since
MuonNavigationSchool assumes both geometry providing classes have
compatible interfaces.
Merge pull request #3635 from Dr15Jones/GeomConstInterface

Geometry -- Const only access to GeometricSearchTracker Geometry