style: Add missing transition timings to some widgets

This change adds missing transition timings to the following widgets:

- Calendar month selectors
- App grid page arrows
- Page indicators dots from the app grid

Follow-up from https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2309/diffs?commit_id=ec571eb86fce93b3b37306b3478cde24019ce8e9

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2665>

data/theme/gnome-shell-sass/widgets/_app-grid.scss

@@ -121,6 +121,7 @@ $app_icon_size: 96px;
     height: 10px;
     border-radius: 10px; // the same as height&width
     background-color: white;
+    transition-duration: 400ms;
   }
 }
 
@@ -167,6 +168,7 @@ $app_icon_size: 96px;
   width: 24px;
   height: 24px;
   border-radius: 99px;
+  transition-duration: 100ms;
 
   > StIcon { color: $system_fg_color;}
 

data/theme/gnome-shell-sass/widgets/_calendar.scss

@@ -56,6 +56,7 @@
       width: 32px;
       margin: 2px;
       border-radius: $base_border_radius;
+      transition-duration: 100ms;
     }
   }