fix(list): item background transparency

Author: MPopov

projects/igniteui-angular/src/lib/core/styles/themes/schemas/dark/_list.scss

@@ -63,12 +63,19 @@ $_dark-indigo-list: extend(
 
         item-background-hover: (
             igx-color: ('primary', 500),
-            rgba: .5
+            rgba: .5,
+            to-opaque: (
+                igx-color: 'surface',
+            )
+
         ),
 
         item-background-active: (
             igx-color: ('primary', 500),
-            rgba: .5
+            rgba: .5,
+            to-opaque: (
+                igx-color: 'surface',
+            )
         )
     )
 );

projects/igniteui-angular/src/lib/core/styles/themes/schemas/light/_list.scss

@@ -214,12 +214,18 @@ $_indigo-list: extend(
 
         item-background-hover: (
             igx-color: ('primary', 500),
-            rgba: .15
+            rgba: .15,
+            to-opaque: (
+                igx-color: 'surface',
+            )
         ),
 
         item-background-active: (
             igx-color: ('primary', 500),
-            rgba: .15
+            rgba: .15,
+            to-opaque: (
+                igx-color: 'surface',
+            )
         ),
 
         item-text-color: (