normalized 16bit texture format support

It seems that webgpu spec and the latest dawn implementation started supporting new 16bit (u|s)norm texture formats.

Maybe I can do this myself and request pull.

But what is the typical procedure to do this? Are you using some script to automate things?

https://www.w3.org/TR/webgpu/#enumdef-gputextureformat
https://github.com/search?q=repo%3Agoogle%2Fdawn%20R16Unorm&type=code