Add distributed DBSCAN verification

[aprokop]

• Refactor existing DBSCAN verification to allow it to work with both local and distributed cases
• Add (partial) distributed DBSCAN verification
  The missing part is making sure cluster IDs are unique. For local, it uses DFS. Don't know how to implement it in distributed.

[aprokop]

The DistributedTree's deduction guide cannot be compiled here by NVCC. In other places it compiles. No idea why, but not spending time to investigate.

[aprokop]

Unrelated (but real) failure on SYCL:

Running 240 test cases...
/var/jenkins/workspace/ArborX_PR-1218/test/tstQueryTreeComparisonWithBoost.cpp(188): error: in "ComparisonWithBoost/boost_rtree_spatial_predicate<TreeExecutionAndMemorySpaces<ArborX_Legacy_BVH_KDOP18_double_ Kokkos__Device<Kokkos__Experimental__SYCL_ Kokkos__Experimental__SYCLDeviceUSMSpace>>>": check query(ExecutionSpace{}, tree, intersects_queries) == (query(ExecutionSpace{}, rtree, intersects_queries_host)) has failed
  - mismatch at position 16: [( ) == ( 228 229 239 240 )] is false

*** 1 failure is detected in the test module "Master Test Suite"

Not going to do anything about it in this PR.