- Add AlertWindow::show() and showAsync() methods that take a MessageBoxOptions argument
  - Add NativeMessageBox::show() and showAsync() methods that take a MessageBoxOptions argument
  - Update the DialogsDemo to demonstrate the new methods
  - Deprecate AlertWindow::showNativeDialogBox() in favour of the NativeMessageBox methods
  - Pass button strings specified in MesssageBoxOptions to native dialog boxes correctly
  - Use modern TaskDialog on Windows for the native dialog box where available

This change adds the examples from `examples/Plugins` to the
AudioPluginHost, surfacing them as 'internal' plugins in the popup menu.

We also build this into the AudioPluginHost, as a convenient way to
check the midi outputs of plugins and devices.