Add Modifiable ptr to the code base

The pointer allows non-const access if the object caring it is also modifiable. Otherwise only const-access is granted

closed

This merge request affects 1 package:

• DetectorDescription/GeoModel/GeoModelUtilities

This merge request affects 2 files:

• DetectorDescription/GeoModel/GeoModelUtilities/GeoModelUtilities/ModifiablePtr.h
• DetectorDescription/GeoModel/GeoModelUtilities/GeoModelUtilities/TransformMap.h

Adding @stavrop ,@jojungge ,@apsallid ,@rbianchi as watchers

added Geometry master review-pending-level-1 labels

CI Result SUCCESS (hash aabed80b)

	Athena	AthSimulation	AthGeneration
externals
cmake
make
tests

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Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 69859]