title: TVirtualStringTree - How to change the [-] / [+] buttons?
body: <p>How can I use my own custom buttons (images) to replace the default <code>[-]</code>/<code>[+]</code> buttons in the VST?<br>
  I want to use arrows instead (<img src="https://i.stack.imgur.com/dpWiD.png" alt="enter image description here">, <img src="https://i.stack.imgur.com/hEuLl.png" alt="enter image description here">), but also to support RTL bidi mode (<img src="https://i.stack.imgur.com/Z1p5k.png" alt="enter image description here">, <img src="https://i.stack.imgur.com/0X2WF.png" alt="enter image description here">).</p>
  
  <p>edit: I am aware of the <code>bsTriangle</code> style (ButtonStyle). It does not respect RTL. I want to use my own custom images.</p>