jw/pkg/cmds/distro/CmdPkg: Add distro pkg ls

Add the distro subcommand class CmdPkg, together with a first
subcommand ls, which prints a list of files contained in a package.

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/cmds/distro/backend/BePkg.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import annotations
+from typing import TYPE_CHECKING
+
+import abc
+from typing import Iterable
+
+from .Backend import Backend as Base
+
+if TYPE_CHECKING:
+    from ..CmdPkg import CmdPkg as Parent
+
+class BePkg(Base):
+
+    def __init__(self, parent: Parent):
+        super().__init__(parent)
+
+    async def list_files(self, name: str) -> Iterable[str]:
+        return await self._list_files(name)
+
+    @abc.abstractmethod
+    async def _list_files(self, name: str) -> Iterable[str]:
+        pass