[FEA] Lanczos solver v2 (rapidsai#2481)

I unfortunately don't have permissions to push on @aamijar branch for the previous Lanczos solver PR (rapidsai#2416) so I kept his commits and continued it here.

## Lanczos Solver for Sparse Eigen Decomposition
We propose a new lanczos solver in raft that fixes the issues present in the previous solver `raft::sparse::solver::detail::computeSmallestEigenvectors`.

Specifically we address the following issues:
1. Numerical Stability for both float32 and float64 datatypes
2. Efficiency and Speed of Convergence

This new implementation is taken from the cupy library `cupyx.scipy.sparse.linalg.eigsh` where the thick-restart and full reorthogonalzation methods are used.

Additionally this PR exposes a python api for raft lanczos solver with an interface similar to `scipy.sparse.linalg.eigsh` and `cupyx.scipy.sparse.linalg.eigsh`.

```py3
from pylibraft.solver import eigsh
```

Authors:
  - Micka (https://github.com/lowener)
  - Anupam (https://github.com/aamijar)
  - Corey J. Nolet (https://github.com/cjnolet)

Approvers:
  - Kyle Edwards (https://github.com/KyleFromNVIDIA)
  - Corey J. Nolet (https://github.com/cjnolet)

URL: rapidsai#2481

cpp/CMakeLists.txt

@@ -268,6 +268,10 @@ if(RAFT_COMPILE_LIBRARY)
     src/raft_runtime/random/rmat_rectangular_generator_int64_float.cu
     src/raft_runtime/random/rmat_rectangular_generator_int_double.cu
     src/raft_runtime/random/rmat_rectangular_generator_int_float.cu
+    src/raft_runtime/solver/lanczos_solver_int64_double.cu
+    src/raft_runtime/solver/lanczos_solver_int64_float.cu
+    src/raft_runtime/solver/lanczos_solver_int_double.cu
+    src/raft_runtime/solver/lanczos_solver_int_float.cu
   )
   set_target_properties(
     raft_objs

cpp/include/raft/sparse/linalg/detail/cusparse_utils.hpp

@@ -30,7 +30,25 @@ namespace linalg {
 namespace detail {
 
 /**
- * @brief create a cuSparse dense descriptor
+ * @brief create a cuSparse dense descriptor for a vector
+ * @tparam ValueType Data type of vector_view (float/double)
+ * @tparam IndexType Type of vector_view
+ * @param[in] vector_view input raft::device_vector_view
+ * @returns dense vector descriptor to be used by cuSparse API
+ */
+template <typename ValueType, typename IndexType>
+cusparseDnVecDescr_t create_descriptor(raft::device_vector_view<ValueType, IndexType> vector_view)
+{
+  cusparseDnVecDescr_t descr;
+  RAFT_CUSPARSE_TRY(raft::sparse::detail::cusparsecreatednvec(
+    &descr,
+    vector_view.extent(0),
+    const_cast<std::remove_const_t<ValueType>*>(vector_view.data_handle())));
+  return descr;
+}
+
+/**
+ * @brief create a cuSparse dense descriptor for a matrix
  * @tparam ValueType Data type of dense_view (float/double)
  * @tparam IndexType Type of dense_view
  * @tparam LayoutPolicy layout of dense_view