So that the same code could possibly be cherry-picked back into 21.0 without
having to set up a separate MR for that.

deal with performing a sparse build on top of any base project. So far
only tested with Athena and AnalysisBase though.

JetSubStructureUtils: various cleanups

See merge request !479

Migrate thread-safe magnetic field service into master

Closes ATLASSIM-3239

See merge request !475

add package G4HiveEx to master

See merge request !442

Muon data handle migration.

See merge request !498

Migrate DCMathSegmentMaker and MuonPatternSegmentMaker to use data handles.
Fix copy and paste of property name in TrigMuonEF.

Fix linking of LArCellRec in dbg build

See merge request !445

SiClusterOnTrackTool: Fix linking in dbg build.

See merge request !457

TrigTruthEventAthenaPool: Fix for finding out-of-repository test reference files.

See merge request !451

add package CaloHiveEx to master

See merge request !431

Add the AthExHive package to master

See merge request !430

DerivationFrameworkJetEtMiss: Fix linking in dbg build.

See merge request !463

TrigT1EventAthenaPool: Fix tests for out-of-repository reference files.

See merge request !465

TrkAlignGenTools: Fix linking in dbg build.

See merge request !458

TrigMinBiasMonitoring: Fix linking in dbg build.

See merge request !459

StoreGate: Introduce a separate lock for the remaps table, to prevent deadlocks.

See merge request !464

Change InDetTrigParticleCreatorTool used for FTK to be the same as for FTF

See merge request !476

eflowAthenaPool: Fix tests for out-of-repository reference files.

See merge request !466

Sherpa_i: Fix linking in dbg build.

See merge request !467

Fixes for GMSB SUSY, Monopole and Qball Simulation

See merge request !435

Simplify varhandle initialization for handles that are possibly ignored.

See merge request !441

CxxUtils: Add macros to checker_macros.h for file pragmas.

See merge request !443

xAODCore: Suppress ubsan warning.

See merge request !444

InDetTrackSelectionTool: Fix compilation with gcc7 and clang warnings

See merge request !468

L2 TrigmuComb algorithm re-tuned matching windows to improve barrel efficiency

See merge request !472

Fix run-time import warnings

See merge request !481

EventBookkeeperAthenaPool: Fix tests to find out-of-repository reference files.

See merge request !450

TileEventAthenaPool: Fix tests to find out-of-repository reference files.

See merge request !447

TrigSteeringEventAthenaPool: Fix tests for finding out-of-repository reference files.

See merge request !446

LArSimEventAthenaPool: Fix tests to find out-of-repository reference files.

See merge request !449

MuonSimEventAthenaPool: Fix tests to find out-of-repository reference files.

See merge request !448

TauTagTools: Fix linking in dbg build.

See merge request !456

eflowRec: Fix linking in dbg build.

See merge request !455

JetRecTools: Fix linking in dbg build.

See merge request !454

RootCollection: Fix linking in dbg build.

See merge request !453

Fix for the FTK RegionSelector (gets q431 working)

Closes ATR-15963

See merge request !488

Original patch from Mark Sutton:

- Update from the very old ID RegionSelector table creation to create the actual
correct new FTK RS tables, and retrieve the correct tool from in the RegSelSvc.

- Remove the obsolete DeltaZ range parameter in the ID tables.

- Should fix https://its.cern.ch/jira/browse/ATR-15963

Blocking copyright edits were fixed and a few other minor issues
spotted by the reviewers of the original MR:
https://gitlab.cern.ch/atlas/athena/merge_requests/429