message: Use the modern event.buttons API TerminalAceViewer
diff: @@ -1034,14 +1034,11 @@ export class TerminalViewer extends ViewerElement implements SupportsClipboardPa
  return;
  }
  - // FIXME use the 'buttons' API.
  - const button = ev.button !== undefined ? ev.button : (ev.which !== undefined ? ev.which - 1 : null);
  -
  - // send the button
  + // send the buttons
  const options: TermApi.MouseEventOptions = {
  - leftButton: button === 0,
  - middleButton: button === 1,
  - rightButton: button === 2,
  + leftButton: (ev.buttons & 1) !== 0,
  + middleButton: (ev.buttons & 4) !== 0,
  + rightButton: (ev.buttons & 2) !== 0,
  ctrlKey: ev.ctrlKey,
  shiftKey: ev.shiftKey,
  metaKey: ev.metaKey,
  