Add support for Python type parameter lists

Sphinx has partial support for type parameter lists: they are supported
by the Python domain in signatures, but are not supported by autodoc.

This adds the following support:

- Sphinx Python domain for type parameter fields in docstrings, with
  sphinx.ext.napoleon support as well.

- Support for type parameters as Sphinx objects, with cross-linking, like
  the existing support for function parameters as Sphinx objects.

- Support in apigen for PEP 695 type parameters, and for displaying
  pre-PEP 695 separately-defined TypeVar types as PEP 695 type parameters.

sphinx_immaterial/apidoc/object_description_options.py

@@ -50,7 +50,22 @@ def format_object_description_tooltip(
     ("py:property", {"toc_icon_class": "alias", "toc_icon_text": "P"}),
     ("py:attribute", {"toc_icon_class": "alias", "toc_icon_text": "A"}),
     ("py:data", {"toc_icon_class": "alias", "toc_icon_text": "V"}),
-    ("py:parameter", {"toc_icon_class": "sub-data", "toc_icon_text": "p"}),
+    (
+        "py:parameter",
+        {
+            "toc_icon_class": "sub-data",
+            "toc_icon_text": "p",
+            "generate_synopses": "first_sentence",
+        },
+    ),
+    (
+        "py:typeParameter",
+        {
+            "toc_icon_class": "alias",
+            "toc_icon_text": "T",
+            "generate_synopses": "first_sentence",
+        },
+    ),
     ("c:member", {"toc_icon_class": "alias", "toc_icon_text": "V"}),
     ("c:var", {"toc_icon_class": "alias", "toc_icon_text": "V"}),
     ("c:function", {"toc_icon_class": "procedure", "toc_icon_text": "F"}),

sphinx_immaterial/apidoc/object_toc.py

@@ -73,7 +73,6 @@ def _make_section_from_field(
         source: docutils.nodes.field,
     ) -> Optional[docutils.nodes.section]:
         fieldname = cast(docutils.nodes.field_name, source[0])
-        fieldbody = cast(docutils.nodes.field_body, source[1])
         ids = fieldname["ids"]
         if not ids:
             # Not indexed