docs/qapi-domain: add "Arguments:" field lists

This adds special rendering for Sphinx's typed info field lists.

This patch does not add any QAPI-aware markup, rendering, or
cross-referencing for the type names, yet. That feature requires a
subclass to TypedField which will happen in its own commit quite a bit
later in this series; after all the basic fields and objects have been
established first.

The syntax for this field is:

:arg type name: description
   description cont'd

You can omit the type or the description. You should not omit the name;
if you do so, it degenerates into a "normal field list" entry, and
probably isn't what you want.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-16-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/sphinx/qapi_domain.py

@@ -33,6 +33,7 @@ from sphinx.domains import (
 from sphinx.locale import _, __
 from sphinx.roles import XRefRole
 from sphinx.util import logging
+from sphinx.util.docfields import TypedField
 from sphinx.util.nodes import make_id, make_refnode
 
 
@@ -273,7 +274,18 @@ class QAPIObject(QAPIDescription):
 class QAPICommand(QAPIObject):
     """Description of a QAPI Command."""
 
-    # Nothing unique for now! Changed in later commits O:-)
+    doc_field_types = QAPIObject.doc_field_types.copy()
+    doc_field_types.extend(
+        [
+            # :arg TypeName ArgName: descr
+            TypedField(
+                "argument",
+                label=_("Arguments"),
+                names=("arg",),
+                can_collapse=False,
+            ),
+        ]
+    )
 
 
 class QAPIModule(QAPIDescription):