add some overloads based on literal values (#293)

stubs/matplotlib/figure.pyi

@@ -14,6 +14,8 @@ from .transforms import BboxBase
 from .axes import Axes
 from .artist import Artist, _finalize_rasterization, allow_rasterization
 from mpl_toolkits.mplot3d import Axes3D
+from .projections.geo import AitoffAxes, HammerAxes, LambertAxes, MollweideAxes
+from .projections.polar import PolarAxes
 
 class _AxesStack:
     def __init__(self) -> None: ...
@@ -73,6 +75,16 @@ class FigureBase(Artist):
     @overload
     def add_subplot(self, *args, projection: Literal['3d'], **kwargs) -> Axes3D: ...
     @overload
+    def add_subplot(self, *args, projection: Literal['aitoff'], **kwargs) -> AitoffAxes: ...
+    @overload
+    def add_subplot(self, *args, projection: Literal['hammer'], **kwargs) -> HammerAxes: ...
+    @overload
+    def add_subplot(self, *args, projection: Literal['lambert'], **kwargs) -> LambertAxes: ...
+    @overload
+    def add_subplot(self, *args, projection: Literal['mollweide'], **kwargs) -> MollweideAxes: ...
+    @overload
+    def add_subplot(self, *args, projection: Literal['polar'], **kwargs) -> PolarAxes: ...
+    @overload
     def add_subplot(self, *args, **kwargs) -> Axes: ...
     @overload
     def subplots(