Fixed #29942 -- Restored source file linking in docs by using the Sphinx linkcode ext.

Co-authored-by: David Smith <smithdc@gmail.com>
Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>

tests/sphinx/testdata/package/__init__.py

@@ -0,0 +1,2 @@
+# This file should never get imported. If it is, then something failed already.
+raise Exception

tests/sphinx/testdata/package/import_error.py

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+from .....test import Test  # noqa
+
+
+class MyClass:
+    pass

tests/sphinx/testdata/package/module.py

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+"""
+Example docstring
+"""
+
+from django.utils.functional import cached_property
+from tests.sphinx.testdata.package.wildcard_module import *  # noqa
+
+from . import other_module  # noqa
+from .other_module import MyOtherClass  # noqa
+
+
+class MyClass(object):
+    def __init__(self):
+        pass
+
+    def my_method(self):
+        pass
+
+    @cached_property
+    def my_cached_property(self):
+        pass
+
+
+def my_function(self):
+    pass

tests/sphinx/testdata/package/other_module.py

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+class MyOtherClass:
+    pass

tests/sphinx/testdata/package/wildcard_base.py

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+class WildcardMixin:
+    pass

tests/sphinx/testdata/package/wildcard_module.py

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+from .wildcard_base import WildcardMixin  # noqa
+
+
+class WildcardClass:
+    pass