Consider changing gpu-supported-limits to a record

[MendyBerger]

Consider changing gpu-supported-limits to a record.

This would allow us to use gpu-supported-limits in gpu-device-descriptor.limits and remove record-option-gpu-size64, as record-option-gpu-size64 feels a bit unnatural.

webgpu.h also seems to be using the same WGPULimits for WGPUDeviceDescriptor.WGPULimits and wgpuAdapterGetLimits.

webgpu.h makes each field optional through special UNDEFINED values.
I don't think we need to make the fields optional in our case, they can just default to the default values listed at https://www.w3.org/TR/webgpu/#supported-limits.

[MendyBerger]

I don't think we need to make the fields optional in our case, they can just default to the default values listed at https://www.w3.org/TR/webgpu/#supported-limits.

That's actually not true yet, as we don't yet have default values in records (WebAssembly/component-model#15).

If we wanna do it now, we'll need to make it a record where every item is an option. And if we do that, gpu-adapter.limits will return a record where everything is an option even though every item is expected to be set. Not ideal.

Probably worth waiting for default values.