Modernize mock stubs (#5949)

* Import from `collections.abc`, instead of `typing`.
* Replace `Text` with `str`.
* Remove version checks.
* Convert mock into a package

stubs/mock/@tests/stubtest_allowlist.txt

@@ -1,7 +1,4 @@
 mock.NonCallableMock.__new__
-mock.NonCallableMock.assert_called
-mock.NonCallableMock.assert_called_once
-mock.NonCallableMock.assert_called_once_with
-mock.NonCallableMock.assert_called_with
-mock.NonCallableMock.assert_not_called
 mock.patch
+mock.mock.NonCallableMock.__new__
+mock.mock.patch