Update to 0.18 and HDR tutorial

First let's go over some of the changes that occurred:

1. RenderPassDescriptor now have 2 new fields: occlusion_query_set and, timestamp_writes. I'm setting both to None for now.
2. ComputePassDescriptor now has a timestamp_writes field.
3. InstanceDescriptor now has some more fields, but I opted to just use ..Default::default() for all the fields other than backends.

HDR tutorial

I've been unsure how best to introduce compute shaders as they are a big part of what makes WebGPU special, but most browsers don't support them at the moment. With Chrome rolling out support for WebGPU, I felt more confident writing a tutorial for them.

Also, I'm been interested learning how to load HDR images from places like Polyhaven, so I decided to introduce compute shaders by creating one that will load an HDR and convert it to a Cubemap to be rendered.

You can check it out here!