Make all module_utils and plugin_utils private (#887)

* Add leading underscore. Remove deprecated module utils.

* Document module and plugin utils as private. Add changelog fragment.

* Convert relative to absolute imports.

* Remove unnecessary imports.

plugins/plugin_utils/_gnupg.py

@@ -0,0 +1,56 @@
+# Copyright (c) 2023, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# Note that this plugin 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
+
+import typing as t
+from subprocess import PIPE, Popen
+
+from ansible.module_utils.common.process import get_bin_path
+from ansible.module_utils.common.text.converters import to_native
+from ansible_collections.community.crypto.plugins.module_utils._gnupg.cli import (
+    GPGError,
+    GPGRunner,
+)
+
+
+class PluginGPGRunner(GPGRunner):
+    def __init__(self, executable: str | None = None, cwd: str | None = None) -> None:
+        if executable is None:
+            try:
+                executable = get_bin_path("gpg")
+            except ValueError:
+                raise GPGError("Cannot find the `gpg` executable on the controller")
+        self.executable = executable
+        self.cwd = cwd
+
+    def run_command(
+        self, command: list[str], check_rc: bool = True, data: bytes | None = None
+    ) -> tuple[int, str, str]:
+        """
+        Run ``[gpg] + command`` and return ``(rc, stdout, stderr)``.
+
+        If ``data`` is not ``None``, it will be provided as stdin.
+        The code assumes it is a bytes string.
+
+        Returned stdout and stderr are native Python strings.
+        Pass ``check_rc=False`` to allow return codes != 0.
+
+        Raises a ``GPGError`` in case of errors.
+        """
+        command = [self.executable] + command
+        p = Popen(
+            command, shell=False, cwd=self.cwd, stdin=PIPE, stdout=PIPE, stderr=PIPE
+        )
+        stdout, stderr = p.communicate(input=data)
+        stdout_n = to_native(stdout, errors="surrogate_or_replace")
+        stderr_n = to_native(stderr, errors="surrogate_or_replace")
+        if check_rc and p.returncode != 0:
+            raise GPGError(
+                f'Running {" ".join(command)} yielded return code {p.returncode} with stdout: "{stdout_n}" and stderr: "{stderr_n}")'
+            )
+        return t.cast(int, p.returncode), stdout_n, stderr_n