Optimize _PyCFunction_FastCallKeywords()

Issue #29259: Write fast path in _PyCFunction_FastCallKeywords() for
METH_FASTCALL, avoid the creation of a temporary dictionary for keyword
arguments.

Cleanup also _PyCFunction_FastCallDict():

* Don't dereference func before checking that it's not NULL
* Move code to raise the "no keyword argument" exception into a new
  no_keyword_error label.

Update python-gdb.py for the change.

Tools/gdb/libpython.py

@@ -1518,7 +1518,8 @@ class Frame(object):
             except RuntimeError:
                 return 'PyCFunction invocation (unable to read "func")'
 
-        elif caller == '_PyCFunction_FastCallDict':
+        elif caller in {'_PyCFunction_FastCallDict',
+                        '_PyCFunction_FastCallKeywords'}:
             try:
                 func = older._gdbframe.read_var('func_obj')
                 return str(func)