Merge pull request matplotlib#22490 from anntzer/ui

Deprecate unused, untested Affine2D.identity().

Author: QuLogic

doc/api/next_api_changes/deprecations/22490-AL.rst

@@ -0,0 +1,4 @@
+``Affine2D.identity()``
+~~~~~~~~~~~~~~~~~~~~~~~
+... is deprecated in favor of directly calling the `.Affine2D` constructor with
+no arguments.

lib/matplotlib/transforms.py

@@ -1958,6 +1958,7 @@ def set(self, other):
         self.invalidate()
 
     @staticmethod
+    @_api.deprecated("3.6", alternative="Affine2D()")
     def identity():
         """
         Return a new `Affine2D` object that is the identity transform.