Adding metadata getter methods to datasets API (#3821)

Closes #3820 

This PR adds simple getter methods to the `dataset` class, which allows users to easily get information about datasets without need to access the `metadata` dict or look in the directory.

```python
from cugraph.datasets import karate

# users now call
karate.number_of_nodes()

# instead of 
karate.metadata['number_of_nodes']
```

Authors:
  - ralph (https://github.com/nv-rliu)

Approvers:
  - Alex Barghi (https://github.com/alexbarghi-nv)

URL: #3821

python/cugraph/cugraph/datasets/dataset.py

@@ -266,6 +266,42 @@ def get_path(self):
 
         return self._path.absolute()
 
+    def is_directed(self):
+        """
+        Returns True if the graph is a directed graph.
+        """
+        return self.metadata["is_directed"]
+
+    def is_multigraph(self):
+        """
+        Returns True if the graph is a multigraph.
+        """
+        return self.metadata["is_multigraph"]
+
+    def is_symmetric(self):
+        """
+        Returns True if the graph is symmetric.
+        """
+        return self.metadata["is_symmetric"]
+
+    def number_of_nodes(self):
+        """
+        An alias of number_of_vertices()
+        """
+        return self.number_of_vertices()
+
+    def number_of_vertices(self):
+        """
+        Get the number of vertices in the graph.
+        """
+        return self.metadata["number_of_nodes"]
+
+    def number_of_edges(self):
+        """
+        Get the number of edges in the graph.
+        """
+        return self.metadata["number_of_edges"]
+
 
 def download_all(force=False):
     """

python/cugraph/cugraph/tests/utils/test_dataset.py

@@ -328,6 +328,16 @@ def test_is_multigraph(dataset):
     assert G.is_multigraph() == dataset.metadata["is_multigraph"]
 
 
+@pytest.mark.parametrize("dataset", ALL_DATASETS)
+def test_object_getters(dataset):
+    assert dataset.is_directed() == dataset.metadata["is_directed"]
+    assert dataset.is_multigraph() == dataset.metadata["is_multigraph"]
+    assert dataset.is_symmetric() == dataset.metadata["is_symmetric"]
+    assert dataset.number_of_nodes() == dataset.metadata["number_of_nodes"]
+    assert dataset.number_of_vertices() == dataset.metadata["number_of_nodes"]
+    assert dataset.number_of_edges() == dataset.metadata["number_of_edges"]
+
+
 #
 # Test experimental for DeprecationWarnings
 #