These files, and several snippets of other files, are generated by Dawn (Chromium's WebGPU library):
The C header is mostly the same as the "upstream"
webgpu.h,
but native-specific elements are not included.
The C++ files are currently Dawn-specific, but included in Emscripten for
better compatibility with Dawn: it has roughly the same API as Dawn's copy, but
is included here because it is strongly tied to an exact webgpu.h revision.
Dawn additionally autogenerates two "snippets" that are used in Emscripten:
library_webgpu_enum_tables.js, which is pasted intolibrary_webgpu.jswebgpu_struct_info.json, which is pasted intostruct_info.json.