Reorganize source files

[aprokop]

Fix #1068.

[dalg24]

I would put ArborX_SpaceFillingCurves.hpp and ArborX_MortonCode.hpp in spatial/

[aprokop]

Had to rename two files, as we had both ArborX_[Details]Dendrogram.hpp and ArborX_[Details]MinimumSpanningTree.hpp.

[aprokop]

Status as of 71fb106:

src/
├── ArborX.hpp
├── ArborX_Config.hpp.in
├── ArborX_Version.hpp.in
├── cluster
│   ├── ArborX_DBSCAN.hpp
│   ├── ArborX_Dendrogram.hpp
│   ├── ArborX_HDBSCAN.hpp
│   ├── ArborX_MinimumSpanningTree.hpp
│   └── detail
│       ├── ArborX_BoruvkaHelpers.hpp
│       ├── ArborX_CartesianGrid.hpp
│       ├── ArborX_DendrogramHelpers.hpp
│       ├── ArborX_FDBSCAN.hpp
│       ├── ArborX_FDBSCANDenseBox.hpp
│       ├── ArborX_MutualReachabilityDistance.hpp
│       ├── ArborX_UnionFind.hpp
│       └── ArborX_WeightedEdge.hpp
├── distributed
│   ├── ArborX_DistributedTree.hpp
│   └── detail
│       ├── ArborX_DistributedTreeImpl.hpp
│       ├── ArborX_DistributedTreeNearest.hpp
│       ├── ArborX_DistributedTreeNearestHelpers.hpp
│       ├── ArborX_DistributedTreeSpatial.hpp
│       ├── ArborX_DistributedTreeUtils.hpp
│       └── ArborX_Distributor.hpp
├── geometry
│   ├── ArborX_Box.hpp
│   ├── ArborX_GeometryTraits.hpp
│   ├── ArborX_KDOP.hpp
│   ├── ArborX_Point.hpp
│   ├── ArborX_Ray.hpp
│   ├── ArborX_Segment.hpp
│   ├── ArborX_Sphere.hpp
│   ├── ArborX_Tetrahedron.hpp
│   ├── ArborX_Triangle.hpp
│   └── detail
│       └── ArborX_GeometryAlgorithms.hpp
├── interpolation
│   ├── ArborX_InterpMovingLeastSquares.hpp
│   └── detail
│       ├── ArborX_InterpDetailsCompactRadialBasisFunction.hpp
│       ├── ArborX_InterpDetailsMovingLeastSquaresCoefficients.hpp
│       ├── ArborX_InterpDetailsPolynomialBasis.hpp
│       └── ArborX_InterpDetailsSymmetricPseudoInverseSVD.hpp
├── kokkos_ext
│   ├── ArborX_KokkosExtAccessibilityTraits.hpp
│   ├── ArborX_KokkosExtArithmeticTraits.hpp
│   ├── ArborX_KokkosExtKernelStdAlgorithms.hpp
│   ├── ArborX_KokkosExtMinMaxReduce.hpp
│   ├── ArborX_KokkosExtSort.hpp
│   ├── ArborX_KokkosExtStdAlgorithms.hpp
│   ├── ArborX_KokkosExtUninitializedMemoryAlgorithms.hpp
│   ├── ArborX_KokkosExtVersion.hpp
│   └── ArborX_KokkosExtViewHelpers.hpp
├── misc
│   ├── ArborX_Containers.hpp
│   ├── ArborX_Exception.hpp
│   ├── ArborX_Heap.hpp
│   ├── ArborX_OperatorFunctionObjects.hpp
│   ├── ArborX_PriorityQueue.hpp
│   ├── ArborX_SortUtils.hpp
│   ├── ArborX_Stack.hpp
│   ├── ArborX_Utils.hpp
│   └── ArborX_Vector.hpp
└── spatial
    ├── ArborX_BruteForce.hpp
    ├── ArborX_CrsGraphWrapper.hpp
    ├── ArborX_LinearBVH.hpp
    └── detail
        ├── ArborX_AccessTraits.hpp
        ├── ArborX_AttachIndices.hpp
        ├── ArborX_BatchedQueries.hpp
        ├── ArborX_BruteForceImpl.hpp
        ├── ArborX_Callbacks.hpp
        ├── ArborX_CrsGraphWrapperImpl.hpp
        ├── ArborX_ExpandHalfToFull.hpp
        ├── ArborX_HalfTraversal.hpp
        ├── ArborX_HappyTreeFriends.hpp
        ├── ArborX_IndexableGetter.hpp
        ├── ArborX_MortonCode.hpp
        ├── ArborX_NearestBufferProvider.hpp
        ├── ArborX_NeighborList.hpp
        ├── ArborX_Node.hpp
        ├── ArborX_PairValueIndex.hpp
        ├── ArborX_PermutedData.hpp
        ├── ArborX_PredicateHelpers.hpp
        ├── ArborX_Predicates.hpp
        ├── ArborX_SpaceFillingCurves.hpp
        ├── ArborX_TraversalPolicy.hpp
        ├── ArborX_TreeConstruction.hpp
        ├── ArborX_TreeNodeLabeling.hpp
        ├── ArborX_TreeTraversal.hpp
        └── ArborX_TreeVisualization.hpp

[dalg24]

Please make sure you hit "squash merge"