Update localization in Pin and Unpin actions

Refactor localization strings in `PinToStartAction.cs` and `UnpinFromStartAction.cs` to use a centralized `Strings` class. This change replaces hardcoded string keys for the `Label` and `Description` properties, improving maintainability and consistency across the application.

Author: mrashutoshnigam

src/Files.App/Actions/Start/PinToStartAction.cs

@@ -12,10 +12,10 @@ internal sealed class PinToStartAction : IAction
 		public IContentPageContext context;
 
 		public string Label
-			=> "PinItemToStart/Text".GetLocalizedResource();
+			=> Strings.PinItemToStart_Text.GetLocalizedResource();
 
 		public string Description
-			=> "PinToStartDescription".GetLocalizedResource();
+			=> Strings.PinToStartDescription.GetLocalizedResource();
 
 		public RichGlyph Glyph
 			=> new(themedIconStyle: "App.ThemedIcons.FavoritePin");

src/Files.App/Actions/Start/UnpinFromStartAction.cs

@@ -12,10 +12,10 @@ internal sealed class UnpinFromStartAction : IAction
 		public IContentPageContext context;
 
 		public string Label
-			=> "UnpinItemFromStart/Text".GetLocalizedResource();
+			=> Strings.UnpinItemFromStart_Text.GetLocalizedResource();
 
 		public string Description
-			=> "UnpinFromStartDescription".GetLocalizedResource();
+			=> Strings.UnpinFromStartDescription.GetLocalizedResource();
 
 		public RichGlyph Glyph
 			=> new(themedIconStyle: "App.ThemedIcons.FavoritePinRemove");