Setting opacity for selected elements does not make them see through

[hamza-hajji]

Describe the bug

If I set an element as selected and set its opactiy, it is not see through

To Reproduce
Steps to reproduce the behavior:

1. Go to https://xeokit.github.io/xeokit-sdk/examples/buildings/#xkt_vbo_Duplex
2. Set an element as selected entity.selected = true
3. Set is opacity to 0.5
4. It's opaque

Expected behavior

In 2.4.x, it is see through, but that behavior changed in 2.5.x

Screenshots

viewer.scene.input.on("mousedown", (coords) => {
  const hit = viewer.scene.pick({
    pickSurface: true,
    canvasPos: coords,
  });

  if (hit) {
    hit.entity.selected = true;
    hit.entity.opacity = 0.5;
  }
});

[xeolabs]

This is a duplicate of #1335

It's only happening for batched triangle geometries using VBO scene representation.

A workaround for now is to enable data textures, for which this does not happen - see this example: https://xeokit.github.io/xeokit-sdk/examples/buildings/#xkt_dtx_RACHouse