Enable GPUExternalTexture on WebGPU?

[seancribbs]

In the future, we want to be able to render video frames into our scene in the browser. I noticed that the WebGPU spec has a type GPUExternalTexture that can be extracted from a <video> element, but there's no analog in wgpu::BindingType.

Obviously, there are limitations in exposing backend-specific APIs while remaining platform-neutral, but how might one go about adding this feature specifically for the WebGPU backend? Can we do it with conditional compilation or is there some existing API we can leverage? Would a pull-request implementing this feature be appreciated or is it low on the priority list?

[i509VCB]

Hi, I've opened #3145 related to this issue. It would cover support for video elements on web.