spawner/unspawner cannot be run directly on windows

[wmmc88]

Describe the bug
The spawner executable in the controller_manager package cannot be run on windows.

To Reproduce
Several related issues:

Using spawner.py works but you get a deprecation warning:

❯ ros2 run controller_manager spawner.py joint_state_broadcaster --controller-manager /controller_manager
C:\Users\melvi\git-repos\ros2_upstream_ws\install\lib\controller_manager\spawner.py:204: DeprecationWarning: 'spawner.py' is deprecated, please use 'spawner' (without .py extension)
  warnings.warn(

Using spawner directly results in a conflict in ros2run:

❯ ros2 run controller_manager spawner joint_state_broadcaster --controller-manager /controller_manager
Multiple executables found:
- C:\Users\melvi\git-repos\ros2_upstream_ws\install\lib\controller_manager\spawner
- C:\Users\melvi\git-repos\ros2_upstream_ws\install\lib\controller_manager\spawner.py

launching spawner from ros2launch using the following snippet fails:

joint_state_broadcaster_spawner := Node(
        package="controller_manager",
        executable="spawner",
        arguments=["joint_state_broadcaster", "--controller-manager", "/controller_manager"],
    )

[ERROR] [spawner.PY-3]: exception occurred while executing process:
Traceback (most recent call last):
  File "C:\dev\ros2_rolling\install\Lib\site-packages\launch\actions\execute_local.py", line 540, in __execute_process
    transport, self._subprocess_protocol = await async_execute_process(
  File "C:\dev\ros2_rolling\install\Lib\site-packages\osrf_pycommon\process_utils\async_execute_process_asyncio\impl.py", line 139, in async_execute_process
    transport, protocol = await _async_execute_process_nopty(
  File "C:\dev\ros2_rolling\install\Lib\site-packages\osrf_pycommon\process_utils\async_execute_process_asyncio\impl.py", line 45, in _async_execute_process_nopty
    transport, protocol = await loop.subprocess_exec(
  File "C:\python38\lib\asyncio\base_events.py", line 1630, in subprocess_exec
    transport = await self._make_subprocess_transport(
  File "C:\python38\lib\asyncio\windows_events.py", line 389, in _make_subprocess_transport
    transp = _WindowsSubprocessTransport(self, protocol, args, shell,
  File "C:\python38\lib\asyncio\base_subprocess.py", line 36, in __init__
    self._start(args=args, shell=shell, stdin=stdin, stdout=stdout,
  File "C:\python38\lib\asyncio\windows_events.py", line 885, in _start
    self._proc = windows_utils.Popen(
  File "C:\python38\lib\asyncio\windows_utils.py", line 153, in __init__
    super().__init__(args, stdin=stdin_rfd, stdout=stdout_wfd,
  File "C:\python38\lib\subprocess.py", line 858, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "C:\python38\lib\subprocess.py", line 1311, in _execute_child
    hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
OSError: [WinError 193] %1 is not a valid Win32 application

Expected behavior
Spawner is launcher without errors or warnings

Environment (please complete the following information):

• OS: Windows
• Version: master
• Anything that may be unusual about your environment

Additional context
The issue looks like its because the spawner script is using a shebang which isn't properly supported in windows. If the desired behaviour is to be able to use spawner instead of the deprecated spawner.py, the script should be installed as a console_script using ament_python_install_package. Changes needed to do this would be similar to ros/xacro#304