gh-113317: Don't use global clinic instance in bad_argument() (#114330)

Make it possible for a converter to have multiple includes, by collecting
them in a list on the converter instance. This implies converter includes
are added during template generation, so we have to add them to the
clinic instance at the end of the template generation instead of in the
beginning.

Tools/clinic/clinic.py

@@ -818,12 +818,6 @@ class CLanguage(Language):
             del parameters[0]
         converters = [p.converter for p in parameters]
 
-        # Copy includes from parameters to Clinic
-        for converter in converters:
-            include = converter.include
-            if include:
-                clinic.add_include(include.filename, include.reason,
-                                   condition=include.condition)
         if f.critical_section:
             clinic.add_include('pycore_critical_section.h', 'Py_BEGIN_CRITICAL_SECTION()')
         has_option_groups = parameters and (parameters[0].group or parameters[-1].group)
@@ -1367,6 +1361,13 @@ class CLanguage(Language):
                                             declarations=declarations)
 
 
+        # Copy includes from parameters to Clinic after parse_arg() has been
+        # called above.
+        for converter in converters:
+            for include in converter.includes:
+                clinic.add_include(include.filename, include.reason,
+                                   condition=include.condition)
+
         if new_or_init:
             methoddef_define = ''
 
@@ -2988,7 +2989,6 @@ class CConverter(metaclass=CConverterAutoRegister):
     # Only set by self_converter.
     signature_name: str | None = None
 
-    include: Include | None = None
     broken_limited_capi: bool = False
 
     # keep in sync with self_converter.__init__!
@@ -3008,6 +3008,7 @@ class CConverter(metaclass=CConverterAutoRegister):
         self.name = ensure_legal_c_identifier(name)
         self.py_name = py_name
         self.unused = unused
+        self.includes: list[Include] = []
 
         if default is not unspecified:
             if (self.default_type
@@ -3263,8 +3264,7 @@ class CConverter(metaclass=CConverterAutoRegister):
         else:
             if expected_literal:
                 expected = f'"{expected}"'
-            if clinic is not None:
-                clinic.add_include('pycore_modsupport.h', '_PyArg_BadArgument()')
+            self.add_include('pycore_modsupport.h', '_PyArg_BadArgument()')
             return f'_PyArg_BadArgument("{{{{name}}}}", "{displayname}", {expected}, {{argname}});'
 
     def format_code(self, fmt: str, *,
@@ -3336,9 +3336,8 @@ class CConverter(metaclass=CConverterAutoRegister):
 
     def add_include(self, name: str, reason: str,
                     *, condition: str | None = None) -> None:
-        if self.include is not None:
-            raise ValueError("a converter only supports a single include")
-        self.include = Include(name, reason, condition)
+        include = Include(name, reason, condition)
+        self.includes.append(include)
 
 type_checks = {
     '&PyLong_Type': ('PyLong_Check', 'int'),