feat: Add support for python-wheel data directory

This feature addes  attribute to the py_wheel rule and
makes a related change to the wheelmaker tool.

Fixes bazelbuild#1777

tests/py_wheel/py_wheel_tests.bzl

@@ -46,6 +46,32 @@ def _test_metadata_impl(env, target):
 
 _tests.append(_test_metadata)
 
+def _test_data(name):
+    rt_util.helper_target(
+        py_wheel,
+        name = name + "_data",
+        distribution = "mydist_" + name,
+        version = "0.0.0",
+        data_files = {
+            "source_name": "wheel_name",
+        },
+    )
+    analysis_test(
+        name = name,
+        impl = _test_data_impl,
+        target = name + "_data",
+    )
+
+def _test_data_impl(env, target):
+
+    action = env.expect.that_target(target).action_named(
+        "PyWheel",
+    )
+    action.contains_at_least_args(["--data_files", "wheel_name;tests/py_wheel/source_name"])
+    action.contains_at_least_inputs(["tests/py_wheel/source_name"])
+
+_tests.append(_test_data)
+
 def _test_content_type_from_attr(name):
     rt_util.helper_target(
         py_wheel,