Added option to set idle time before cursor is hidden (Ryujinx#4390)

In SettingsWindow.cs and SettingsWindow.glade:
Replaced Always/On Idle/Never radio buttons with a dropdown (combo box).
When selecting "On Idle", a "Seconds" label and numeric text box (spinner) appear.  The spinner is limited 1-10.

In ConfigurationFileFormat.cs and ConfigurationState.cs, and SettingsViewModel.cs:
Load the saved value, or default 5 seconds if no value exists.
Save the custom set value to the config file.

In SettingsViewModel.cs:
Catch when the idle time setting is changed while a game is running, and change the value live.

src/Ryujinx.UI.Common/Configuration/ConfigurationFileFormat.cs

@@ -172,6 +172,11 @@ namespace Ryujinx.UI.Common.Configuration
         /// </summary>
         public HideCursorMode HideCursor { get; set; }
 
+        /// <summary>
+        /// How many seconds to wait before hiding the cursor when set to hide on idle
+        /// </summary>
+        public int HideCursorIdleTime { get; set; }
+
         /// <summary>
         /// Enables or disables Vertical Sync
         /// </summary>