Type annotation add_subplot for projection="3d"

Author: stefanv

lib/matplotlib/figure.pyi

@@ -1,3 +1,7 @@
+from typing import TYPE_CHECKING
+if TYPE_CHECKING:
+    import mpl_toolkits
+
 from collections.abc import Callable, Hashable, Iterable, Sequence
 import os
 from typing import Any, IO, Literal, TypeVar, overload
@@ -87,6 +91,8 @@ class FigureBase(Artist):
 
     # TODO: docstring indicates SubplotSpec a valid arg, but none of the listed signatures appear to be that
     @overload
+    def add_subplot(self, *args, projection="3d", **kwargs) -> mpl_toolkits.mplot3d.Axes3D: ...
+    @overload
     def add_subplot(
         self, nrows: int, ncols: int, index: int | tuple[int, int], **kwargs
     ) -> Axes: ...