feat: Add support for gamepad control of ImGui

Alongside a settings option and the ability for plugins to query gamepad state.
PLugins cannot, however, as of now set an input as 'handled' and block it
for the game.
Whether game or ImGui is receiving gamepad input can be be checked via
`(ImGui.GetIO().ConfigFlags & ImGuiConfigFlags.NavEnableGamepad) > 0`

Dalamud/Configuration/DalamudConfiguration.cs

@@ -122,6 +122,11 @@ namespace Dalamud.Configuration
         /// </summary>
         public bool IsDisableViewport { get; set; } = true;
 
+        /// <summary>
+        /// Gets or sets a value indicating whether or not navigation via a gamepad should be globally enabled in ImGui.
+        /// </summary>
+        public bool IsGamepadNavigationEnabled { get; set; } = true;
+
         /// <summary>
         /// Load a configuration from the provided path.
         /// </summary>