Add tests for xrefs on Python and JavaScript domains

These are just the passing test cases for the domains currently. I am going to
patch up issues with nesting on both domains to start, so these are the test
cases I'll be testing against. I'll see about addressing the other core
domains, or at very least the cpp domain, with similar tests if this looks
okay.

So far, these tests only test against methods/functions for the basic nesting
structure. More complete tests will test additional domain roles.

Refs #662

tests/roots/test-domain-py/roles.rst

@@ -0,0 +1,48 @@
+roles
+=====
+
+.. py:class:: TopLevel
+
+.. py:method:: top_level
+
+* :py:class:`TopLevel`
+* :py:meth:`top_level`
+
+
+.. py:class:: NestedParentA
+
+    * Link to :py:meth:`child_1`
+
+    .. py:method:: child_1()
+
+        * Link to :py:meth:`NestedChildA.subchild_2`
+        * Link to :py:meth:`child_2`
+        * Link to :any:`any_child`
+
+    .. py:method:: any_child()
+
+        * Link to :py:class:`NestedChildA`
+
+    .. py:class:: NestedChildA
+
+        .. py:method:: subchild_1()
+
+            * Link to :py:meth:`subchild_2`
+
+        .. py:method:: subchild_2()
+
+            Link to :py:meth:`NestedParentA.child_1`
+
+    .. py:method:: child_2()
+
+        Link to :py:meth:`NestedChildA.subchild_1`
+
+.. py:class:: NestedParentB
+
+    * Link to :py:meth:`child_1`
+
+    .. py:method:: child_1()
+
+        * Link to :py:class:`NestedParentB`
+
+* :py:class:`NestedParentA.NestedChildA`