Calculate initial GTK window size using logical DPI

Otherwise, if the pixel ratio is changed before the window is created,
the window will be scaled up an extra time. This occurs on GTK3, but not
GTK4, due to some different order of events, but I changed the GTK4
backend to do the same for consistency.

Author: QuLogic

lib/matplotlib/backends/backend_gtk3.py

@@ -340,8 +340,7 @@ def __init__(self, canvas, num):
 
         self.vbox.pack_start(self.canvas, True, True, 0)
         # calculate size for window
-        w = int(self.canvas.figure.bbox.width)
-        h = int(self.canvas.figure.bbox.height)
+        w, h = self.canvas.get_width_height()
 
         self.toolbar = self._get_toolbar()
 

lib/matplotlib/backends/backend_gtk4.py

@@ -287,8 +287,7 @@ def __init__(self, canvas, num):
 
         self.vbox.prepend(self.canvas)
         # calculate size for window
-        w = int(self.canvas.figure.bbox.width)
-        h = int(self.canvas.figure.bbox.height)
+        w, h = self.canvas.get_width_height()
 
         self.toolbar = self._get_toolbar()