wallpapers/image: follow system animation speed setting in wallpaper transition

The value is to keep compatible with the old feeling defined by
"TransitionAnimationDuration" (default: 1000)

BUG: 395324
FIXED-IN: 5.26

wallpapers/image/imagepackage/contents/config/main.xml

@@ -38,10 +38,6 @@
       <label>Interval between slides (s)</label>
       <default>900</default>
     </entry>
-    <entry name="TransitionAnimationDuration" type="int">
-      <label>Fade Transition Animation  (ms)</label>
-      <default>1000</default>
-    </entry>
     <entry name="UncheckedSlides" type="StringList">
       <label>Unchecked Slides</label>
       <default></default>

wallpapers/image/imagepackage/contents/ui/main.qml

@@ -178,16 +178,18 @@ QQC2.StackView {
 
     replaceEnter: Transition {
         OpacityAnimator {
+            id: replaceEnterOpacityAnimator
             from: 0
             to: 1
-            duration: wallpaper.configuration.TransitionAnimationDuration
+            // The value is to keep compatible with the old feeling defined by "TransitionAnimationDuration" (default: 1000)
+            duration: Math.round(PlasmaCore.Units.veryLongDuration * 2.5)
         }
     }
     // Keep the old image around till the new one is fully faded in
     // If we fade both at the same time you can see the background behind glimpse through
     replaceExit: Transition{
         PauseAnimation {
-            duration: wallpaper.configuration.TransitionAnimationDuration
+            duration: replaceEnterOpacityAnimator.duration
         }
     }
 }

wallpapers/image/slideshowpackage/contents/config/main.xml

@@ -30,10 +30,6 @@
       <label>Interval between slides (s)</label>
       <default>900</default>
     </entry>
-    <entry name="TransitionAnimationDuration" type="int">
-      <label>Fade Transition Animation (ms)</label>
-      <default>1000</default>
-    </entry>
     <entry name="UncheckedSlides" type="StringList">
       <label>Unchecked Slides</label>
       <default></default>