Use __init__ type hints in "description" mode

Previously, `__init__` type hints were not used when documenting a class
using `autodoc_typehints="description"`. This was done to prevent
documentation for parameters from showing up twice, but that will no
longer occur now that parameter and return types are only inserted if
the parameter or return has a description.

Closes sphinx-doc#8178

sphinx/ext/autodoc/typehints.py

@@ -42,8 +42,6 @@ def merge_typehints(app: Sphinx, domain: str, objtype: str, contentnode: Element
         return
     if app.config.autodoc_typehints != 'description':
         return
-    if objtype == 'class' and app.config.autoclass_content not in ('init', 'both'):
-        return
 
     try:
         signature = cast(addnodes.desc_signature, contentnode.parent[0])