`add_signal_handler` support for all platforms

Feature or enhancement

Proposal:

I'm currently writing this to support signals on Windows and Linux:

loop = asyncio.get_running_loop()

def shutdown(*args):
    // some shutdown sequence

if sys.platform == "win32":
    for sig in (signal.SIGINT, signal.SIGTERM):
        signal.signal(sig, shutdown)
else:
    for sig in (signal.SIGINT, signal.SIGTERM):
        loop.add_signal_handler(sig, shutdown)

Works great, but why would signal.signal be supported on Linux and Windows, but asyncio's AbstractEventLoop via add_signal_handler only on Linux? Can't this be platform agnostic?

add_signal_handler would raise the following on Windows:

[...]\Python\Python313\Lib\asyncio\events.py", line 596, in add_signal_handler
    raise NotImplementedError

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

asyncio.AbstractEventLoop.add_signal_handler と、Python313/Lib/asyncio/events.py の 596 行目に示されている NotImplementedError から始め、その後 Windows と Linux における signal.signal と比較します。add_signal_handler で要求されたクロスプラットフォーム動作を提供できるかどうかを明らかにし、その結果としてのプラットフォームサポートを文書化または実装できれば完了です。