Synchronize master branch with 2024-patches

Includes:

• Prepare Rec v36r16 (!4122 (merged))
• Modernize TrackParticleMonitor replacing old-style Gaudi histograms with Gaudi::Accumulators::Histogram (!3878 (merged))
• Fix SHARE_BPV functor to not compare addresses of two pointers (!4107 (merged))
• Fix Issue 589: make sure Child returns a reference, and not a copy of the child. (!4114 (merged))
• minimal changes required to make OfflineVertexFitter threadsafe (!4060 (merged))
• Bugfix: Fix the wrong sign of OSelectron tag decision (!4108 (merged))
• Release notes for v36r15 (!4109 (merged))