Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/unittest/suite.pyi

@@ -0,0 +1,20 @@
+import unittest.case
+import unittest.result
+from typing import Iterable, Iterator, List, Union
+
+_TestType = Union[unittest.case.TestCase, TestSuite]
+
+class BaseTestSuite(Iterable[_TestType]):
+    _tests: List[unittest.case.TestCase]
+    _removed_tests: int
+    def __init__(self, tests: Iterable[_TestType] = ...) -> None: ...
+    def __call__(self, result: unittest.result.TestResult) -> unittest.result.TestResult: ...
+    def addTest(self, test: _TestType) -> None: ...
+    def addTests(self, tests: Iterable[_TestType]) -> None: ...
+    def run(self, result: unittest.result.TestResult) -> unittest.result.TestResult: ...
+    def debug(self) -> None: ...
+    def countTestCases(self) -> int: ...
+    def __iter__(self) -> Iterator[_TestType]: ...
+
+class TestSuite(BaseTestSuite):
+    def run(self, result: unittest.result.TestResult, debug: bool = ...) -> unittest.result.TestResult: ...