effects: always use Title Case for user-facing effect titles

Most already did, but these three did not, creating inconsistency.

BUG: 464122
FIXED-IN: 5.27

src/effects/backgroundcontrast/metadata.json

@@ -42,7 +42,7 @@
         "EnabledByDefault": true,
         "Id": "contrast",
         "License": "GPL",
-        "Name": "Background contrast",
+        "Name": "Background Contrast",
         "Name[ar]": "تباين الخلفية",
         "Name[az]": "Fon kontrastı",
         "Name[be]": "Кантраснасць фону",

src/effects/morphingpopups/package/metadata.json

@@ -73,7 +73,7 @@
         "Icon": "preferences-system-windows-effect-morphingpopups",
         "Id": "kwin4_effect_morphingpopups",
         "License": "GPL",
-        "Name": "Morphing popups",
+        "Name": "Morphing Popups",
         "Name[ar]": "المنبثقات المتحورة",
         "Name[be]": "Трансфармаванне выплыўных акон",
         "Name[bg]": "Променящи се изскачащи прозорци",

src/effects/slidingpopups/metadata.json

@@ -42,7 +42,7 @@
         "EnabledByDefault": true,
         "Id": "slidingpopups",
         "License": "GPL",
-        "Name": "Sliding popups",
+        "Name": "Sliding Popups",
         "Name[ar]": "تمرير المنبثقات",
         "Name[az]": "Ani pəncərə animasiyası",
         "Name[be]": "Высоўныя выплыўныя вокны",