Code Quality: Added placeholder content for Shelf (#17058)

Author: yaira2

src/Files.App/Assets/Shelf/EmptyShelf_100_ThemeDark.svg

@@ -238,4 +238,31 @@ protected override Visibility Convert(object? value, object? parameter, string?
 			return new NotSupportedException();
 		}
 	}
+
+	internal sealed partial class EmptyListToVisibilityConverter : ValueConverter<object?, Visibility>
+	{
+		protected override Visibility Convert(object? value, object? parameter, string? language)
+		{
+			return (value is int count && count == 0) ? Visibility.Visible : Visibility.Collapsed;
+		}
+
+		protected override object? ConvertBack(Visibility value, object? parameter, string? language)
+		{
+			return new NotSupportedException();
+		}
+	}
+
+	internal sealed partial class PopulatedListToVisibilityConverter : ValueConverter<object?, Visibility>
+	{
+		protected override Visibility Convert(object? value, object? parameter, string? language)
+		{
+			return (value is int count && count > 0) ? Visibility.Visible : Visibility.Collapsed;
+		}
+
+		protected override object? ConvertBack(Visibility value, object? parameter, string? language)
+		{
+			return new NotSupportedException();
+		}
+	}
 }
+

src/Files.App/Assets/Shelf/EmptyShelf_100_ThemeLight.svg

@@ -4197,6 +4197,9 @@
     <value>Enable Omnibar</value>
   </data>
   <data name="SectionsHiddenMessage" xml:space="preserve">
-    <value>You can add sections to the sidebar by right-clicking and selecting the sections you want to add.</value>
+    <value>You can add sections to the sidebar by right-clicking and selecting the sections you want to add</value>
+  </data>
+  <data name="EmptyShelfText" xml:space="preserve">
+    <value>Drag files or folders here to interact with them across different tabs</value>
   </data>
 </root>

src/Files.App/Assets/Shelf/EmptyShelf_200_ThemeDark.svg

@@ -325,6 +325,7 @@
 		<!--  Right Side Action Buttons  -->
 		<StackPanel
 			Grid.Column="2"
+			Margin="0,0,4,0"
 			Orientation="Horizontal"
 			Spacing="4">