AU and AUv3 plugins only support version numbers with up to 3 parts.

- 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

When loading exporter icons on a background save thread we need to take the MessageManagerLock as the image file may be an SVG which has a message thread dependency in the Drawable parsing code

See BREAKING-CHANGES.txt for more details.

This fixes warnings that are emitted when building with the `-analyze`
flag enabled.