gh-122858: Deprecate asyncio.iscoroutinefunction (#122875)

Deprecate `asyncio.iscoroutinefunction` in favor of `inspect.iscoroutinefunction`.

Co-authored-by: Kumar Aditya <kumaraditya@python.org>

Lib/asyncio/coroutines.py

@@ -18,7 +18,16 @@ _is_coroutine = object()
 
 
 def iscoroutinefunction(func):
+    import warnings
     """Return True if func is a decorated coroutine function."""
+    warnings._deprecated("asyncio.iscoroutinefunction",
+                         f"{warnings._DEPRECATED_MSG}; "
+                         "use inspect.iscoroutinefunction() instead",
+                         remove=(3,16))
+    return _iscoroutinefunction(func)
+
+
+def _iscoroutinefunction(func):
     return (inspect.iscoroutinefunction(func) or
             getattr(func, '_is_coroutine', None) is _is_coroutine)