Use webgpu.yml for parsing

[almarklein]

As a replacement for webgpu.h (webgpu.h is now generated from the yaml). Probably best to wait until wgpu.yml is also ready. See https://github.com/webgpu-native/webgpu-headers/pull/259 for details.

[Korijn]

From that thread:

I might go so far as to say - I'd like to author this in YAML, but downstream projects should consume the JSON instead, and if they add extensions as new files, they may choose to write the extension files as JSON instead of YAML.

Which would be great since we don't need a dep for json.

[almarklein]

BTW we still need the header files for cffi. But we can ditch our manual h-parser code.