Deprecate duplicated FigureManagerGTK{3,4}Agg classes.

This is consistent with other GUI backends: we can just directly use
FigureManagerGTK{3,4}.

Author: anntzer

doc/api/next_api_changes/deprecations/21982-AL.rst

@@ -0,0 +1,4 @@
+``FigureManagerGTK3Agg`` and ``FigureManagerGTK4Agg``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... are deprecated; directly use ``FigureManagerGTK3`` and
+``FigureManagerGTK4`` instead.

lib/matplotlib/backends/backend_gtk3agg.py

@@ -1,6 +1,6 @@
 import numpy as np
 
-from .. import cbook
+from .. import _api, cbook
 try:
     from . import backend_cairo
 except ImportError as e:
@@ -76,11 +76,11 @@ def draw(self):
         backend_gtk3.FigureCanvasGTK3.draw(self)
 
 
+@_api.deprecated("3.6", alternative="backend_gtk3.FigureManagerGTK3")
 class FigureManagerGTK3Agg(backend_gtk3.FigureManagerGTK3):
     pass
 
 
 @_BackendGTK3.export
 class _BackendGTK3Cairo(_BackendGTK3):
     FigureCanvas = FigureCanvasGTK3Agg
-    FigureManager = FigureManagerGTK3Agg

lib/matplotlib/backends/backend_gtk4agg.py

@@ -1,6 +1,6 @@
 import numpy as np
 
-from .. import cbook
+from .. import _api, cbook
 try:
     from . import backend_cairo
 except ImportError as e:
@@ -44,11 +44,11 @@ def draw(self):
         backend_gtk4.FigureCanvasGTK4.draw(self)
 
 
+@_api.deprecated("3.6", alternative="backend_gtk4.FigureManagerGTK4")
 class FigureManagerGTK4Agg(backend_gtk4.FigureManagerGTK4):
     pass
 
 
 @_BackendGTK4.export
 class _BackendGTK4Agg(_BackendGTK4):
     FigureCanvas = FigureCanvasGTK4Agg
-    FigureManager = FigureManagerGTK4Agg