MuPatPrimitives+MuonTrackSteeringTools: Lifetime management update

Have addToTrash return a (bare) pointer to the object just added. Avoids having a pattern in the caller where it looks like a dangling pointer is retained from a unique_ptr.

This merge request affects 2 packages:

• MuonSpectrometer/MuonReconstruction/MuonTrackMakers/MuonTrackMakerTools/MuPatPrimitives
• MuonSpectrometer/MuonReconstruction/MuonTrackMakers/MuonTrackMakerTools/MuonTrackSteeringTools

Affected files list will not be printed in this case

Adding @pscholer ,@goetz ,@kluit ,@stavrop ,@apsallid ,@jojungge ,@mvozak as watchers

added MuonSpectrometer main review-pending-level-1 labels

CI Result SUCCESS (hash b9de08f7)

	Athena
externals
cmake
make
tests

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removed review-pending-level-1 label

added review-approved label

merged

mentioned in commit 9dde8bd2