Deprecate the noop, unused FigureCanvasBase.resize.

Not to be confused with FigureManager.resize, which is implemented and
used by various subclasses.

Author: anntzer

doc/api/next_api_changes/deprecations/22050-AL.rst

@@ -0,0 +1,4 @@
+``FigureCanvasBase.resize``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This method has no effect and is deprecated.  Use ``FigureManagerBase.resize``
+instead.

lib/matplotlib/backend_bases.py

@@ -1679,6 +1679,7 @@ def pick(self, mouseevent):
     def blit(self, bbox=None):
         """Blit the canvas in bbox (default entire canvas)."""
 
+    @_api.deprecated("3.6", alternative="FigureManagerBase.resize")
     def resize(self, w, h):
         """
         UNUSED: Set the canvas size in pixels.