title: Can Firemonkey TTabControl replicate VCL TPageControl.OnChanging event?
body: <p>I'm Running Delphi Dx Seattle</p>
  
  <p>In Delphi VCL's TPageControl there is a onChanging event where you could stop the page control from changing tab's</p>
  
  <pre><code>procedure TForm1.pgc1Changing(Sender: TObject; var AllowChange: Boolean);
  begin
    if MessageDlg('do you want to change tab?', mtConfirmation, [mbyes, mbno], 0, mbNo) = mrno then
      AllowChange := false;
  end;
  </code></pre>
  
  <p>Is there a way for Delphi Firemonkey TTabControl to replicate this?
  e.g.<br>if you have two tabs and clicking on the other tab pops up a question 'do you want to change tab?'<br>
  if you click No nothing happens click yes then it changes</p>