add type annotations for 'docutils.parsers.rst.directives.admonitions' (#12396)

stubs/docutils/@tests/stubtest_allowlist.txt

@@ -10,6 +10,7 @@ docutils.nodes.GenericNodeVisitor.__getattr__
 # these methods take a rawsource parameter that has been deprecated and is completely ignored, so we omit it from the stub
 docutils.nodes.Text.__new__
 docutils.parsers.recommonmark_wrapper
+docutils.parsers.rst.directives.admonitions.BaseAdmonition.node_class  # must be overridden by base classes (pseudo-abstract)
 docutils.parsers.rst.directives.misc.MetaBody.__getattr__
 docutils.statemachine.State.nested_sm  # is initialised in __init__
 docutils.statemachine.State.nested_sm_kwargs  # is initialised in __init__

stubs/docutils/docutils/parsers/rst/directives/admonitions.pyi

@@ -1,3 +1,16 @@
-from _typeshed import Incomplete
+from docutils import nodes
+from docutils.parsers.rst import Directive
 
-def __getattr__(name: str) -> Incomplete: ...
+class BaseAdmonition(Directive):
+    node_class: type[nodes.Admonition]  # Subclasses must set this to the appropriate admonition node class.
+
+class Admonition(BaseAdmonition): ...
+class Attention(BaseAdmonition): ...
+class Caution(BaseAdmonition): ...
+class Danger(BaseAdmonition): ...
+class Error(BaseAdmonition): ...
+class Hint(BaseAdmonition): ...
+class Important(BaseAdmonition): ...
+class Note(BaseAdmonition): ...
+class Tip(BaseAdmonition): ...
+class Warning(BaseAdmonition): ...