[BEAM-7060] Cherry-pick #9562: Prefer inspect module over funcsigs

sdks/python/apache_beam/transforms/core.py

@@ -317,6 +317,8 @@ def get_function_args_defaults(f):
     it doesn't include bound arguments and may follow function wrappers.
   """
   signature = get_signature(f)
+  # Fall back on funcsigs if inspect module doesn't have 'Parameter'; prefer
+  # inspect.Parameter over funcsigs.Parameter if both are available.
   try:
     parameter = inspect.Parameter
   except AttributeError:

sdks/python/apache_beam/typehints/decorators.py

@@ -167,10 +167,12 @@ def get_signature(func):
   latter: 'the "self" parameter is always reported, even for bound methods'
   https://github.com/python/cpython/blob/44f91c388a6f4da9ed3300df32ca290b8aa104ea/Lib/inspect.py#L1103
   """
-  if funcsigs is not None:
-    inspect_ = funcsigs
-  else:
+  # Fall back on funcsigs if inspect module doesn't have 'signature'; prefer
+  # inspect.signature over funcsigs.signature if both are available.
+  if hasattr(inspect, 'signature'):
     inspect_ = inspect
+  else:
+    inspect_ = funcsigs
 
   try:
     signature = inspect_.signature(func)