Revise documentation for file picker control · picoe/Eto@f1c8753

The following actions uses node12 which is deprecated and will be forced to run on node16: actions/checkout@v2, maxim-lobanov/setup-xamarin@v1, actions/upload-artifact@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L14

'Display.DeviceManager' is obsolete

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L14

'DeviceManager.ClientPointer' is obsolete

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L14

'Device.Grab(Window, GrabOwnership, bool, EventMask, Cursor, uint)' is obsolete

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L42

'Display.DeviceManager' is obsolete

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L42

'DeviceManager.ClientPointer' is obsolete

Build: src/Eto.Gtk/CustomControls/WindowExtensions.cs#L42

'Device.Ungrab(uint)' is obsolete