gh-108303: Move all doctest related files and tests to Lib/test/test_doctest/ (#112109)

Co-authored-by: Brett Cannon <brett@python.org>

Lib/test/test_doctest/sample_doctest_no_docstrings.py

@@ -0,0 +1,12 @@
+# This is a sample module used for testing doctest.
+#
+# This module is for testing how doctest handles a module with no
+# docstrings.
+
+
+class Foo(object):
+
+    # A class with no docstring.
+
+    def __init__(self):
+        pass