ARROW-4226: [C++] Add sparse CSF tensor support

This is to resolve [ARROW-4226](https://issues.apache.org/jira/browse/ARROW-4226).

Closes apache#5716 from rok/ARROW-4226 and squashes the following commits:

9ca93ab <Rok> Implementing review feedback.
1b922f6 <Rok> Implementing review feedback.
11b81bb <Rok> Factoring out index incrementing for dense to COO and CSF indices.
6f4f4a8 <Rok> Implementing feedback review.
28d38cb <Rok> Removing backslashes from comments.
3291abc <Rok> Marking indptrBuffers, indicesBuffers and axisOrder required.
d9ff47e <Rok> Further work and implementing review feedback.
24a831f <Rok> Style.
4f2bf00 <Rok> Work on CSF index tests.
6ceb406 <Rok> Implementing review feedback.
bd0d8c2 <Rok> Dense to sparse CSF conversion now in order of dimension size.
eb51947 <Rok> Switching SparseCSFIndex to '2D' data structure.
a322ff5 <Rok> Adding tests for multiple index value types for SparseCSFIndex.
f44d92c <Rok> Adding SparseCSFIndex::Make.
7d17995 <Rok> Adding Tensor to SparseCSFTensor conversion.
05a47a5 <Rok> Using axis_order in CSF.
6b938f7 <Rok> Documentation.
2d10104 <Rok> WIP

Authored-by: Rok <rok@mihevc.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>

cpp/src/arrow/compare.cc

@@ -1196,6 +1196,13 @@ inline bool SparseTensorEqualsImplDispatch(const SparseTensorImpl<SparseIndexTyp
                                                                               right_csc);
     }
 
+    case SparseTensorFormat::CSF: {
+      const auto& right_csf =
+          checked_cast<const SparseTensorImpl<SparseCSFIndex>&>(right);
+      return SparseTensorEqualsImpl<SparseIndexType, SparseCSFIndex>::Compare(left,
+                                                                              right_csf);
+    }
+
     default:
       return false;
   }
@@ -1232,6 +1239,11 @@ bool SparseTensorEquals(const SparseTensor& left, const SparseTensor& right) {
       return SparseTensorEqualsImplDispatch(left_csc, right);
     }
 
+    case SparseTensorFormat::CSF: {
+      const auto& left_csf = checked_cast<const SparseTensorImpl<SparseCSFIndex>&>(left);
+      return SparseTensorEqualsImplDispatch(left_csf, right);
+    }
+
     default:
       return false;
   }

cpp/src/arrow/python/serialize.cc

@@ -654,6 +654,7 @@ Status CountSparseTensors(
   OwnedRef num_sparse_tensors(PyDict_New());
   size_t num_coo = 0;
   size_t num_csr = 0;
+  size_t num_csf = 0;
 
   for (const auto& sparse_tensor : sparse_tensors) {
     switch (sparse_tensor->format_id()) {
@@ -663,6 +664,9 @@ Status CountSparseTensors(
       case SparseTensorFormat::CSR:
         ++num_csr;
         break;
+      case SparseTensorFormat::CSF:
+        ++num_csf;
+        break;
       case SparseTensorFormat::CSC:
         // TODO(mrkn): support csc
         break;
@@ -671,6 +675,7 @@ Status CountSparseTensors(
 
   PyDict_SetItemString(num_sparse_tensors.obj(), "coo", PyLong_FromSize_t(num_coo));
   PyDict_SetItemString(num_sparse_tensors.obj(), "csr", PyLong_FromSize_t(num_csr));
+  PyDict_SetItemString(num_sparse_tensors.obj(), "csf", PyLong_FromSize_t(num_csf));
   RETURN_IF_PYERROR();
 
   *out = num_sparse_tensors.detach();