setScissorRect 在 WebGL 和 WebGPU 下效果不一致

[xiaoiver]

renderPass.setScissorRect(0, 0, 500, 500);

WebGL 和 WebGPU 的坐标原点不同：

setViewport 同理

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Title: setScissorRect has inconsistent effects under WebGL and WebGPU

renderPass.setScissorRect(0, 0, 500, 500);

The coordinate origins of WebGL and WebGPU are different:

[xiaoiver]

固定原点为左下角，在 setViewport / ScissorRect 时，需要换算反转下 Y 轴：

private flipY(y: number, h: number) {
  const height = this.device['swapChainHeight'];
  return height - y - h;
}

[xiaoiver]

另外在读取纹理数据时，WebGL 同样也是从左下角开始，而 WebGPU 从左上角开始，也需要统一 Readback 中的实现

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In addition, when reading texture data, WebGL also starts from the lower left corner, while WebGPU starts from the upper left corner, and the implementation in Readback also needs to be unified.