Examples: Improve WebGPURenderer with antialias: true

[linbingquan]

Related issue: #XXXX

Description

As the title.

[linbingquan]

@sunag Why there WebGPU examples does not enable the antialias flag. Maybe WebGPURenderer does not support it or I am miss something about it.

three.js/examples/webgpu_cubemap_dynamic.html

Line 65 in 391c8ce

renderer = new WebGPURenderer( /*{ antialias: true }*/ );

three.js/examples/webgpu_backdrop_area.html

Line 126 in 391c8ce

renderer = new WebGPURenderer( /*{ antialias: true }*/ );

[sunag]

The example has an incompatibility with the Renderer.copyFramebufferToTexture() method, this can be fixed, I just commented so I could merger the PR, the other example I think I commented by mistake.