build.cmds: Move build.App.cmd_xxx() here

For every cmd_xxx() method in build.App, create a class that's
instatiated for running the respective command. This has the
advantage of making App.py smaller (and faster), and having smaller,
more maintainable command modules adhering to a common interface.

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

src/python/jw/build/cmds/CmdPkgProvides.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+
+from argparse import Namespace, ArgumentParser
+
+from ..Cmd import Cmd
+
+class CmdPkgProvides(Cmd): # export
+
+    def __init__(self) -> None:
+        super().__init__('pkg-provides', help='Print packages and capabilities provided a given package')
+
+    def add_arguments(self, parser: ArgumentParser) -> None:
+        self.app.pkg_relations_add_arguments(parser)
+        super().add_arguments(parser)
+
+    def _run(self, args: Namespace) -> None:
+        return self.app.print_pkg_relations("provides", args)