Make all doc fragments, module utils, and plugin utils private (#11896)

* Make all doc fragments private.

* Make all plugin utils private.

* Make all module utils private.

* Reformat.

* Changelog fragment.

* Update configs and ignores.

* Adjust unit test names.

plugins/module_utils/_module_helper.py

@@ -0,0 +1,24 @@
+# (c) 2020, Alexei Znamensky <russoz@gmail.com>
+# Copyright (c) 2020, Ansible Project
+# Simplified BSD License (see LICENSES/BSD-2-Clause.txt or https://opensource.org/licenses/BSD-2-Clause)
+# SPDX-License-Identifier: BSD-2-Clause
+
+# Note that this module util is **PRIVATE** to the collection. It can have breaking changes at any time.
+# Do not use this from other collections or standalone plugins/modules!
+
+from __future__ import annotations
+
+# pylint: disable=unused-import
+from ansible_collections.community.general.plugins.module_utils._mh.deco import (  # noqa: F401
+    cause_changes,
+    check_mode_skip,
+    check_mode_skip_returns,
+    module_fails_on_exception,
+)
+from ansible_collections.community.general.plugins.module_utils._mh.exceptions import (
+    ModuleHelperException,  # noqa: F401
+)
+from ansible_collections.community.general.plugins.module_utils._mh.module_helper import (  # noqa: F401
+    ModuleHelper,
+    StateModuleHelper,
+)